It is good for a person to be part of a church, whether denominational or non-denominational. Our Lord is to Jesus Christ, no matter what church we belong to.
It is certainly good to have fellowship...but it is interesting that "church" has come to mean the gathering place rather than the people of God. To be part of THE church we have to be born again, while if we are not born again, no amount of gathering in a building will make us so: we have to come to Jesus ourselves, lay our lives down, trust Him for forgiveness and cleansing if all our sin, repenting of all we know to be wrong, and ask Him to come into our hearts and lives and make us new.
That done, we are born again, and we are therefore free to gather where the Lord sends us:John 3:8 The wind bloweth where it listeth, and thou hearest the sound thereof, but canst not tell whence it cometh, and whither it goeth:
so is every one that is born of the Spirit.
...and He will be the orchestrator and initiator of all fellowship and ministry.
We need not worry about numbers because Jesus says where 2 or 3 are gathered in His name, He is among us...so we can know His presence individually with His Spirit residing in us, and also as a group when we gather. My personal view is that a small group of true believers is much better for us than any mega church where we can get swallowed up in the throng, or ignored when we have needs. Also it us harder to tell when a large group has gone astray from the word because there tends to be some element of control exerted via the leadership to keep order according to doctrine and the service format, and not according to the Spirit.
Some years ago facing trouble in a local assembly (concealed adultery in the leadership which God wanted revealed) I found myself lied about, preached against and more or less kicked out...even though it was proven beyond all doubt that what God was showing me was happening there was true. I reluctantly left, but found that the Lord opened up to me His view of the church through the comfort of scripture, and scriptural comparisons of true and false brethren. It wasn't what I thought it was.
When Jesus says "ye shall know them by their fruits" it is because the true church is not plainly obvious, and doesn't consist of everyone who says they are His. We have to seek out and identify the true ones for fellowship and then give what we can according to ministerial needs arising, and assist all to function likewise. I have a few brothers and sisters locally but nowhere to meet formally...though that may change at some point.
I think there is a real problem if we do church the way it has always been done, just because it has always been done that way. Traditions have a negative effect on the working of God through His word as Jesus told the pharisees in Mark 7:13
Making the word of God of none effect through your tradition, which ye have delivered: and many such like things do ye.
