Ephesians "one body, one faith...was written in context to the church at Ephesus. Not universal.
Incorrect, it is a universal statement, applied to their local situation. Paul is basically saying, "because the whole church body encompasses believers in Christ everywhere (that's universal), your own local assembly at Ephesus (that's local) should seek for unity". This is clear in verses 4 and 5 which refer to one lord and one baptism etc.. I don't think Paul was saying that Christ was only one lord of the Ephesians. It is universal.
Paul's other statements referring to the body is universal referring to Jew and gentile:
Eph 2:16
And that he might reconcile both unto God in one body by the cross, having slain the enmity thereby:
All saved in the family of God
Not all saved in the His church
I think there's a visible church and an invisible church body. All saved are part of the inivisble church body. The visible church includes both tares and wheat.
How can a universal church discipline I corin 7
The universal church disciples by the disciple of the many local churches joined together. Roman Catholics have a strong argument here with the way they are structured - a Pope, Cardinals, Bishops etc.
If all are members of the Bride, who are the guests at the wedding supper of the Lamb?
I think this was covered before in a past discussion. Consult any good bible commentary.
How does au niversal body of believers with all different doctrines( i.e. security of the believer to believe one can loose their salvation, some believe works for salvation and some believed salvation is all of grace etc. ( ever come into the unity of the faith that Paul told the Ephesians church was required?
All mainstream denominations do, or should, hold to the key doctrines of the faith. Many are expressed in creeds such as the Nicene or Apostle's creed.
Topics such as can you lose your salvation have no bearing on whether someone is a christian or part of the body of Christ. Two sides of the same coin.