Just some thoughts to explore:

(From message #1)“Why were Jesus’ followers allowed to continue in Jerusalem, more-or-less without persecution?”
Is there credible evidence that this was the case? They hid, in fear of their lives, at the very least until the feast of Pentecost. Even after that point, one of them was, killed on the streets. That’s the only example we’re given, but to decide from that story that there was indeed only one who died is arguing from silence, and not reasoned discourse. An equally reasonable conclusion from those facts would be that they continued on in the face of danger, risking their lives for what they believed in.
“a reasoned argument cannot rely on just one source”
Depends upon whether one is arguing a posteriori or a priori doesn’t it? ;{>} But the more interesting question would be is the bible one source, or is it rather a collection of different sources, gathered together for handy reference? What you’ve written here seems to imply the latter, as you differentiate Paul from the Gospel writers. If it’s true the bible is only one source, then what are the grounds for differentiating what Paul is supposed to have written from what Peter or Matthew are supposed to have written? And if there’s a reason for differentiating them, then how can the bible be considered a single source?
“they were Jewish in their practices yet had a belief in the risen Jesus”
Groups such as they exist today. In today’s jargon they are often called “messianic” or “completed” jews.
The question before the early church was how to handle converts who had not been jews before joining them. Those who were jews continued with the laws they had been following, recognizing in Jesus the promised Messiah. Should they compel those who hadn’t been jews first to become jews, and only then accept them? Or should they be admitted under a different banner? It caused quite a discussion, but they concluded the latter should be the case.
“should I, as a Christian, be following Jewish law if I want to practice a Christianity that is as Christ wanted, and not as Paul wanted?”
An important question. But, as with all “either/or” questions, one whose basic assumptions need to be questioned.
Question: Is there credible evidence that Paul’s version is different from Christ’s version? Yes, Christ was born and raised a jew. But he was also charged with the violation of many jewish laws, and had unpleasant things to say about the religious leaders of his day, and on at least one occasion barely escaped stoning for blasphemy by those who listened to him. Doesn’t sound on the face of it that he was all that committed to following jewish law and custom.
Given the above, and given that James and Peter, the one his brother and the other part of the “inner circle” of his followers, both supported Paul’s version, it would seem there is enough evidence to assume that the version Paul preached was not substantively different from the version Jesus had preached. To deny that assumption, I think we’d need to some evidence that they were willing to overthrow the teachings of Jesus in favor of a johnny-come-lately who had never met Jesus in the flesh.
Remember, if Paul altered the message to make it more palatable to Rome, there exists sufficient evidence to indict him for incompetence, given his own (and Peter’s) death at the hands of Rome. That should have been enough to completely discredit his approach, and the remaining followers would have returned to what had been taught before, had it really been different. And if not that, then Nero, Domitian, and the persecution of the early church would certainly have resulted in the abandonment of Paul’s version, had it really been sanitized for Rome’s approval.