You make good points, all mostly true. I hope you have been reading various things and just didn't hear these all from some Christian-basher. Yes they are true but . . .
I'm not a Christian so I am not going to give you an answer based on doctrine or even my own belief.
The fact is, there is a separation between Jesus and his life and his teachings (if he even existed) and the things that were said about him and taught about him and taught in his name after he was gone. You have to see them as two different things. And you have to argue against them with two different arguments.
Yes, Paul doesn't mention the Gospels in his epistles. You probably know why. Because Paul's epistles predate the gospels chronologically--the gospels hadn't been written yet!
No, there is no contemporary historical evidence of Jesus' existence. But this is true for the great majority of people who lived then. The only individual people we really know about are Roman Emperors and a few other powerful politicians.
But to me (Non-Christian, remember) what's important is Jesus's teachings. They are self-evident. They are good teachings! You could do worse than to believe in them and live by them. (Sometimes I wish more Christians would learn about them!)
Maybe Jesus was really a 'composite' character, there had to be several ascetic Jewish loners who traveled around and did magic tricks and taught about the brotherhood of man. Maybe he was just made up. To me, it doesn't even really matter. To a Christian it would matter, but that's just -them-. 8^)
Jesus would often tell a story to answer a question. A 'parable'. Were these stories true? I have had Christians tell me they must be true. They were in the Bible, weren't they? They have to be literally true.
But think about it, the purpose of the story is to make a point. For it to do that, it's not necessary for the story to be true. Jesus could have made them up, they'd be just as good for their purpose, don't you think? The story of the Boy who Cried Wolf was told to children for centuries to teach them why you shouldn't make false alarms. Did it ever really happen? I would guess not, I would guess it was made up. It's still a good story, though, and it illustrates the point.
That's how I see the life of Jesus. Whether Jesus is a 'legend' based on truth, a composite, or never existed at all, his following became legion, and his cult became the official religion of the Roman Empire and later of all of Europe. His story and teachings have become one of the bases of Western Culture. They are significant even if he is a fictional character like Robin Hood or Sherlock Holmes.