Silas/Silvanus helped Paul evangelize Europe (1 Thess 1:1; 2 Cor 1:19; Acts 16:19-29; 17:10,14-15; 18:5). Paul even mentions him ahead of Timothy (1 Thess 1:1; 2 Cor 1:19). All this shows that there can have been no significant ideological difference between the two men on the issue of Gentile liberty. Yet we also read that Silas was a leader in the Judean church and that he represented the church of Jerusalem on this very issue (Acts 15:22-34; 15:40). The apostles and elders sent Silas to Antioch to represent their views on the issue of Gentile inclusion so we can assume that Silas's views were similar to theirs. Furthermore, Silvanus is attested by "Peter" in 1 Peter 5:12. So Paul's views = Silas's views = Jerusalem's views, therefore Paul's views = Jerusalem's views. In any case, a big gulf between Paul and the Jerusalem church leaders is problematic.
Prisca and Aquila had almost certainly come to the faith independently of Paul's missionary work (Acts 18:2-3). They were from Italy, where Paul had not been. If Paul had a gospel that was at variance with the wider church, as many suppose, it would be hard to explain why Paul collaborated so closely with Prisca and Aquila. He stayed with them (Acts 18:3). They risked their necks for him (Rom 16:3) and he gives them the position of honor at the top of the list of those in Rome whom he greets, and they headed a house church in Ephesus (1 Cor 16:19), presumably with Paul's approval.
Andronicus and Junia came to the faith independently of Paul (Rom 16:6-7), yet he esteems them highly and recognizes their apostleship. They had probably been in prison together.
Apollos was from Alexandria and had clearly not inherited his faith via Paul (Acts 18:24). While there were some in Corinth who claimed to belong to Apollos (1 Cor 1:12), Paul recognized the important role that Apollos had played (1 Cor 3:6). Paul makes no distinctions between the various parties in Corinth, including the "Paul" party, but is critical of the divisions. While there may have been some theological differences between Paul and Apollos (Acts 18:25-19:7), the issue of Gentile liberty was not one of them. Circumcision and Law observance are hardly mentioned in 1 Corinthians (1 Cor 7:18-19), so Apollos had not encouraged the Corinthians to Judaiz.
It seems that there were some in Corinth who claimed allegiance to Peter (1 Cor 1:12). If Paul and Peter had distinct theologies on Gentile inclusion, we would expect Paul to bring up the issue in 1 Corinthians, but he does not.
Luke was clearly an admirer of both Peter and Paul. This is hard to explain if, as some suppose, there was a Paul camp and a Peter camp, representing distinctly different ideologies.
Clement of Rome reveres Peter and Paul in the same breath:
Take the noble figures of our won generation. Even the greatest and most virtuous pillars of our Church were assailed by envy and jealousy, and had to keep up the struggle till death ended their days. Look at the good Apostles. It was by sinful jealousy that Peter was subjected to tribulation, not once or twice but many times; it was in that way that he bore his witness, ere he left for his well-earned place in glory. And Paul, because of jealousy and contention, has become the very type of endurance rewarded. He was in bonds seven times, he was exiled, he was stoned. He preached in the East and in the West, winning a noble reputation for his faith. He taught righteousness to all the world; and after reaching the furthest limits of the West, and bearing his testimony before kings and rulers, he passed out of this world and was received into the holy places. I him we have one of the greatest of all examples of endurance.
In summary, it seems to me that the evidence outside Galatians suggests that Paul remained firmly within the circle of the mainstream church, as presided over by the Jerusalem church leaders. Those who are determined to see a theological chasm between a Paul camp and the 'pillars' in Jerusalem will no doubt suggest that the lack of evidence for their hypothesis just shows how thoroughly the truth has been suppressed by Luke. However, such a conspiracy would have to have involved not only conscious distortion of the direct data by Luke, but also careful manipulation of subtle incidental details, and deliberate corruption of the undisputed letters of Paul!