Here are the answers to your "initial questions" and others you post.
1: we don't know for sure who instructed Cain and Abel about sacrifice. There are a few speculations. A; God made the initial "sacrifice" by clothing Adam and Eve by sacrificing an animal for them. So they follow suit and start making sacrifices too God. B; God instructed Cain and Abel about sacrifices. We don't know for sure as this is the first mention of sacrifice in the Bible.
Well, if the first speculation is true, then, again, how did Abel and Cain know about the same? They obviously weren't even yet alive at that point in time, so somebody, whether God, their parents or an angel, must have informed them of the same. In any case, speculations aside, what was the purpose of sacrifices if not to foreshadow the crucifixion of Christ "the Lamb slain from the foundation of the world" (Revelation 13:8) or to foreshadow that we are "redeemed...with the precious blood of Christ, as of a lamb, without blemish and without spot: Who verily was foreordained before the foundation of the world, but was manifest in these last times for us" (I Peter 1:18-20)? Answer this for me, if you would be so kind. There is what is commonly referred to as "a scarlet thread" which weaves its way throughout the Old Testament in that there are many types and shadows of Christ's redeeming blood throughout the Old Testament, including said sacrifices, and, therefore, when John the Baptist said of Jesus, "Behold the Lamb of God which taketh away the sin of the world" (John 1:29), the people should have known exactly what John was talking about.
2: Since Christ, Jesus or Messiah are never mentioned before this then faith would have been in God the Father.
You're splitting hairs here. We both know that God mentioned a coming Redeemer in Genesis 3:15, so if this coming Redeemer wasn't Christ, then Who was He? Also, again, if Abel's sacrifice wasn't meant to foreshadow Christ's ultimate sacrifice, then why was sacrifice established to begin with? Again, we know that Christ was foreordained before the foundation of the world to be "the Lamb of God which taketh away the sin of the world" and we know that sacrifices such as the Passover and others all pointed directly to Christ, so what did Abel's sacrifice point to which he offered "by faith" if not to Christ? I find it interesting, to say the least, that you're attributing Abel's righteousness to merely a belief in God when God Himself has determined that none are righteous apart from Christ all throughout scripture.
God the Father is the only person of the trinity who speaks to man through the OT.
Christ is heard speaking a truckload of times in the Old Testament, so you really ought to spend a lot less time trying to "correct" me when I'm speaking the truth and a lot more time prayerfully studying your Bible. I could give you many examples of the same, but I'll just give you two for now:
"For both he that sanctifieth and they who are sanctified are all of one: for which cause he is not ashamed to call them brethren, Saying, I will declare thy name unto my brethren, in the midst of the church will I sing praise unto thee. And again, I will put my trust in him. And again, Behold I and the children which God hath given me." (Hebrews 2:11-13)
Jesus is "not ashamed to call them", Christians, "brethren" and He said as much in the Old Testament right here:
"I will declare thy name unto my brethren: in the midst of the congregation will I praise thee." (Psalm 22:22)
Furthermore, Jesus spoke in the Old Testament about both "Himself and the children which God had given Him":
"Behold, I and the children whom the LORD hath given me are for signs and for wonders in Israel from the LORD of hosts, which dwelleth in mount Zion." (Isaiah 8:18)
I could easily give you many, many more examples of the same, so for you to say that "God the Father is the only person of the trinity who speaks to man through the OT" only shows how your time would be much better spent in learning how to properly read and understand the Bible than it would be spent in attempting to "correct" me when I'm not even in error to begin with.
The idea of Adam and Eve knowing what Gen 3:15 is refering too is pure speculation as it is never mentioned that they understood this.
Again, God mentioned a coming Redeemer. If you want to believe that Adam and Eve were clueless as to what this meant, then that's certainly your prerogative to do so. I believe otherwise, so we'll just have to disagree on this point.
The title "Christ" is never mentioned in the Bible until Matt 1:1. The title "Messiah" is never mentioned until Dan 9:25. The "Immanuel Prophesy" is never mentioned before Isaiah 7. There is no Biblical proof that Adam and Eve could have taught the kids about Christ (more on this one later). To say that Abel placed his faith in Christ is an absurd stretch of truth.
The title "Christ", Greek "Christos", is the equivalent of "anointed", Hebrew "mashiyach", which appears regularly in the Old Testament scriptures. Here's a clear example of the same:
"Why do the heathen rage, and the people imagine a vain thing? The kings of the earth set themselves, and the rulers take counsel together, against the LORD, and against his anointed (Hebrew: mashiyach), saying, Let us break their bands asunder, and cast away their cords from us." (Psalm 2:1-3, parentheses mine)
"And when they heard that, they lifted up their voice to God with one accord, and said, Lord, thou art God, which hast made heaven, and earth, and the sea, and all that in them is: Who by the mouth of thy servant David hast said, Why did the heathen rage, and the people imagine vain things? The kings of the earth stood up, and the rulers were gathered together against the Lord, and against his Christ (Greek: Christos)." (Acts 4:24-26, parentheses mine)
This mention of the Messiah (Hebrew: mashiyach) certainly appears before Daniel's mention of the same, so, again, I'd advise you to adjust your theology accordingly. In fact, there are multiple mentions of "mashiyachs" in the Old Testament which precede Daniel's mention in that priests, kings and prophets were all "anointed" (Hebrew: mashiyach or Hebrew: mashach which is the root of mashiyach and which means to "anoint") as foreshadowings of the ultimate Priest, King and Prophet, Jesus Christ. I'll just give one example of each from the Old Testament:
"And the priest that is anointed (Hebrew: mashiyach) shall take of the bullock's blood, and bring it to the tabernacle of the congregation:" (Leviticus 4:5, parentheses mine)
" Now these be the last words of David. David the son of Jesse said, and the man who was raised up on high, the anointed (Hebrew: mashiyach) of the God of Jacob, and the sweet psalmist of Israel, said," (II Samuel 23:1, parentheses mine)
"And Jehu the son of Nimshi shalt thou anoint (Hebrew: mashach and the base root of mashiyach) to be king over Israel: and Elisha the son of Shaphat of Abel-meholah shalt thou anoint (Hebrew: mashach and the base root of mashiyach) to be prophet in thy room." (I Kings 19:16, parentheses mine)
The name of Jesus is never mentioned until Matt 1:1.
I wouldn't be too sure of that if I was you:
"And she shall bring forth a son, and thou shalt call his name JESUS: for he shall save his people from their sins." (Matthew 1:21)
Jesus was given His name "for" or because the name Jesus, which is the Greek equivalent of the Hebrew Yeshua, literally means "He shall save His people from their sins" or "Jehovah is salvation":
Online Etymology Dictionary
Jesus
late 12c. (Old English used hælend "savior"), from Greek Iesous, which is an attempt to render into Greek the Aramaic proper name Jeshua
(Hebrew Yeshua) "Jah is salvation," a common Jewish personal name,
the later form of Hebrew Yehoshua (see Joshua).
Not only was Joshua a foreshadowing of Christ both in name and certain deeds, but Jesus' name in its Hebrew equivalent of Yeshua appears regularly in the underlying Hebrew of the Old Testament as our English word "salvation". Again, I'll just give you two examples of the same:
"I have waited for thy salvation (Hebrew: yĕshuw`ah), O LORD." (Genesis 49:18, parentheses mine)
"The LORD is my strength and song, and he is become my salvation (Hebrew: yĕshuw`ah): he is my God, and I will prepare him an habitation; my father's God, and I will exalt him." (Exodus 15:2, parentheses mine)
Furthermore, whereas you wrongly insist that Jesus is never heard speaking in the Old Testament, Paul tells us that Christ was actually the Rock Who followed the Israelites during their wilderness journeys and that He is the One Whom the Israelites tempted:
"Moreover, brethren, I would not that ye should be ignorant, how that all our fathers were under the cloud, and all passed through the sea; And were all baptized unto Moses in the cloud and in the sea; And did all eat the same spiritual meat; And did all drink the same spiritual drink: for they drank of that spiritual Rock that followed them: and that Rock was Christ. But with many of them God was not well pleased: for they were overthrown in the wilderness. Now these things were our examples, to the intent we should not lust after evil things, as they also lusted. Neither be ye idolaters, as were some of them; as it is written, The people sat down to eat and drink, and rose up to play. Neither let us commit fornication, as some of them committed, and fell in one day three and twenty thousand. Neither let us tempt Christ, as some of them also tempted, and were destroyed of serpents. Neither murmur ye, as some of them also murmured, and were destroyed of the destroyer. Now all these things happened unto them for ensamples: and they are written for our admonition, upon whom the ends of the world are come. Wherefore let him that thinketh he standeth take heed lest he fall." (I Corinthians 10:1-12)
Paul said that "the Rock that followed them was Christ" and Moses basically said the same exact thing:
"But Jeshurun waxed fat, and kicked: thou art waxen fat, thou art grown thick, thou art covered with fatness; then he forsook God which made him, and lightly esteemed the Rock of his salvation (Hebrew: yĕshuw`ah)." (Deuteronomy 32:15, parentheses mine)
In effect, Moses spoke of "the Rock of Yeshua" and Paul spoke of "the Rock which was Christ". Is there really any difference? In any case, the Hebrew word "yĕshuw`ah" appears 78 times in 77 verses in the Old Testament and you can verify that for yourself here:
Hebrew Lexicon :: H3444 (KJV)
3&4: you answer these questions in your opening by quoting Heb 11:4. Abel speaks to us "though he died" by his faith in God. It was by his faith by which God "commends as righteous". Abel is one of which is spoken of in Heb 12:1 as part of the "great cloud of witnesses" by which we are deemed as righteous by faith.
And the whole epistle to the Hebrews describes for us the righteousness of God which is by faith in Christ as does the whole New Testament and the whole Old Testament if properly understood. Paul said:
"But now the righteousness of God without the law is manifested, being witnessed by the law and the prophets; Even the righteousness of God which is by faith of Jesus Christ unto all and upon all them that believe: for there is no difference: For all have sinned, and come short of the glory of God; Being justified freely by his grace through the redemption that is in Christ Jesus: Whom God hath set forth to be a propitiation through faith in his blood, to declare his righteousness for the remission of sins that are past, through the forbearance of God; To declare, I say, at this time his righteousness: that he might be just, and the justifier of him which believeth in Jesus." (Romans 3:21-26)
The righteousness of God cannot be separated from faith in Christ Jesus and if you think otherwise, then you are greatly deceived.
(From your question #2) Before Jesus walked this earth, died for our sins and on the third day rose there was no Gospel of Christ.
Paul would certainly disagree with you:
"For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures; And that he was buried, and that he rose again the third day according to the scriptures:" (I Corinthians 15:1-3)
"The scriptures" of which Paul spoke were the Old Testament scriptures and I'll be happy to prove the same to you if need be.
Noah by his faith in God the Father built the ark. Abraham by his faith in God the Father is seen as righteous by his faith. David is known as "a man after God's own heart" by his faith in God the Father. You cannot say there was a Gospel of Christ before the finished Work of Christ. Again, there was no Gospel of Christ before Christ.
Yet again, you don't know what you're talking about. Peter told us what Noah's ark represents when he wrote:
"For Christ also hath once suffered for sins, the just for the unjust, that he might bring us to God, being put to death in the flesh, but quickened by the Spirit: By which also he went and preached unto the spirits in prison; Which sometime were disobedient, when once the longsuffering of God waited in the days of Noah, while the ark was a preparing, wherein few, that is, eight souls were saved by water. The like figure whereunto even baptism doth also now save us (not the putting away of the filth of the flesh, but the answer of a good conscience toward God,) by the resurrection of Jesus Christ: Who is gone into heaven, and is on the right hand of God; angels and authorities and powers being made subject unto him." (I Peter 3:18-22)
Not only did what happened in relation to Noah and the flood prefigure water baptism or "the answer of a good conscience towards God by the resurrection of Jesus Christ from the dead", but Peter also told us that Noah was "a preacher of righteousness":
"And spared not the old world, but saved Noah the eighth person, a preacher of righteousness, bringing in the flood upon the world of the ungodly;" (II Peter 2:5)
Again, what type of righteousness was Noah preaching? You apparently believe that there is a righteousness apart from faith in Christ, but the Bible teaches no such thing unless you're into self-righteousness which counts for nothing in God's sight. Furthermore, as with Abel, we read of Noah's "faith":
"By faith Noah, being warned of God of things not seen as yet, moved with fear, prepared an ark to the saving of his house; by the which he condemned the world, and became heir of the righteousness which is by faith." (Hebrews 11:7)
Again, "Noah became an heir of the righteousness which is by faith" and if you think that anybody is an "heir" without being a "joint-heir with Christ" (Romans 8:17) or that anybody is deemed to be "righteous" in God's eyes apart from "faith in Christ", then you're beyond confused.
Abraham's "faith" was similarly "in Christ" despite your apparent ignorance of the same:
"And the scripture, foreseeing that God would justify the heathen through faith, preached before the gospel unto Abraham, saying, In thee shall all nations be blessed." (Galatians 3:8)
Again:
"Now to Abraham and his seed were the promises made. He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ. And this I say, that the covenant, that was confirmed before of God in Christ, the law, which was four hundred and thirty years after, cannot disannul, that it should make the promise of none effect. For if the inheritance be of the law, it is no more of promise: but God gave it to Abraham by promise. Wherefore then serveth the law? It was added because of transgressions, till the seed should come to whom the promise was made; and it was ordained by angels in the hand of a mediator." (Galatians 3:16-19)
God not only "preached before the gospel unto Abraham" which you apparently believe didn't include Christ, but Abraham's "seed...is Christ" and Abraham was well aware of the same. When God spoke to Abraham in relation to his "seed, which is Christ", He was actually "confirming His covenant in Christ" Who is "the seed Who should come to Whom the promise was made".
Regarding David, I've already shown that David mentioned "the mashiyach" or "the Christ" in Psalm 2, but I'll add this as well:
"While the Pharisees were gathered together, Jesus asked them, Saying, What think ye of Christ? whose son is he? They say unto him, The Son of David. He saith unto them, How then doth David in spirit call him Lord, saying, The LORD said unto my Lord, Sit thou on my right hand, till I make thine enemies thy footstool? If David then call him Lord, how is he his son? And no man was able to answer him a word, neither durst any man from that day forth ask him any more questions." (Matthew 22:41-46)
Jesus here quoted from Psalm 110 in which David called Jesus "Lord", so how the heck could you possibly believe that David didn't know about the gospel of Christ?
I'll finish addressing your post in my next response.