1. I know very little about the apostolic period. Very, very little.
2. For a dude who never seemed to get along well with Peter, and who maybe even didn't really have that high of an official calling, Paul certainly ended up having a lot of influence over orthodox Christian doctrine. Some of that is the result of history; Paul's work survived more completely. Of course, that wasn't just an exogenous event; which writings were preserved and which were suppressed were heavily determined by human favor and disfavor, not just which scrolls didn't fall apart. But Paul's prominence in the New Testament seems incongruous with his prominence in his lifetime. I think all we can definitively say about him is he was a super gung-ho high-profile convert given some missionary assignments. Who just happened to completely reshape Christianity.
3. What if Paul's teachings can best be understood as the higher-level instruction that, without the underlying foundational teachings, can be misleading? Spencer writes about how Paul's time in Corinth was (sorta maybe willfully) misunderstood by the Corinthians, and his first epistle to them was trying to set things right. If Paul's personal ministry could be problematic, what of his mail-order ministry, and what of his posthumous mail-order ministry?
Paul comes along, supposes everyone gets the gospel core, and teaches a bunch of advanced material like the pointlessness of the law. His non-advanced listeners say, "Sweet, licentiousness!" Paul says, "You're misunderstanding me." But once Paul's dead and he can't refute the misinterpretation, his work could have been favored precisely because it was possible to misinterpret it.