In His incarnation ("in the flesh"), He was sent to none but the lost sheep of the house of Israel (Matthew 15:24). We cannot know Him in His capacity of Israel's Messiah (2 Cor 5:16), but only through the revelation of the mystery (Rom 16:25; Eph 3:8-9).
Yes, NOW there is no difference! TODAY there is no difference, and thank God for it! Your problem is, up to and past Acts ch. 10, the wall was still up in the minds of Messianic Jews. Peter was reluctant to even darken a dog Gentile's door (Acts 10:28). Believing Jews were telling only other Jews about Messiah (Acts 11:19). Peter and the rest hadn't yet been told there was no longer a difference between Jews and Gentiles...that means they knew nothing, yet, of the Body of Christ. That knowledge came to them through Paul.
Addressed above.
The core of Paul's "my gospel" is Christ and Him crucified for the sins of the world, without distinction. If you can find Peter preaching that at Pentecost, you'll have a point.
It was not made known to the disciples before it was revealed to Paul. It was made known to them TO and THROUGH Paul (Gal 1:11-12).
Yes there is, in Galatians 2.
The Body of Christ is grafted onto nothing. It is its own entity, complete in Christ, untied from covenant Israel.
Good post!