IMO the strongest evidence for historicity in Paul is the "James, the brother of the Lord" reference in Galatians.
I'm starting to think that Galatians is the most fake book of Paul.
The penny dropped when I read that Paul is not consistent about how we should regard the law. In Romans he supposedly says you should follow it. Christians rely on Galatians totally, for evidence that they don't have to obey the law. Considering that Matthew says that anyone who preaches against the law, will likely be going to hell, it has seemed odd to me, that this easy attack is left lying around on the ground.
Acts is a book that has been fabricated to endorse Paul as a real person. It makes sense that Galatians would also need to be fabricated, to make a link between the Pauline Epistles, Paul and the Church, by his own words. Conveniently, not only does he attach himself to the church, but he also pukes up some critical Christian doctrine. What are the chances of that, in the same small (easily faked) document, without him mentioning it again, in any other epistle? As Paul admonishes the Galatians, there is no real need for him to bring up the Jewish Christian Church, and admit that they oppose his view. It substantially diminishes his argument to them. But, of course, he has no argument to the Galatians, because he didn't write the letter.