Jesus' tomb was robbed. Of course. Jesus' followers, out of a mixture of wishful thinking, superstition, and political expediency, propagated the myth of the Resurrection.
Constantine didn't convert to Christianity. He glorified himself as a God, like all Roman emperors. He co-opted the Jesus myth to aggrandize himself the same way he fancied and promoted himself as the incarnation of Apollo. He did stop persecuting and start ingratiating himself to the Christians because their strong authoritarian structure was politically useful.
Paul never heard a word Jesus said. Everything he preached, going back to the epiphany on the road to Damascus, was a product of his hallucinatory imagination. Everything he said Jesus stood for was stuff Paul heard Jesus saying directly to him in his mind. Much of it directly contravened the Christianity preached by the real apostles Peter and James. Why did and do people put so much stock in what Paul said? Probably just because it was appealing.
The eruption of Vesuvius in 79 AD had more to do with the successful propagation of Christianity than Paul did.
The gospel(s) that assert Jesus prophecied the destruction of the Temple were written after the destruction of the temple.