Yes, he did say that, but that doesn't address the question of why he didn't do that straight away. That would seem to be the obvious thing to do. Yet he swears as if on an oath that he didn't. So he must have had strong reasons for ignoring James and Peter and going to Arabia. That is possibly where he had his revelations, independent of the Jerusalem Church.

Regarding the nature of Jesus, why would James believe that he was God incarnate? Surely he would be more likely to believe that his brother was another family member, and a member of the same religious movement. In any case, it depends who you read. Are you familiar with Robert Eisenman's work on James?

I'm not sure about your next point. I can't remember exactly where it is, but Paul somewhere refers to a different group of apparent 'Christians' who are teaching a different message, and warns his followers to beware of them.