You claim they did but I'm unconvinced. They may well have considered him a spiritual leader and Messiah while he lived and came to believe he was a something more when rumors of his resurrection began to circulate. But early Christians were by no means united in their view of his divinity, some sects believing he was fully human while others considered him fully divine and others staking out a middle ground. It was these disagreements which led to the trinity. In Catholic Christianity, Jesus is both fully human and fully divine. Can God be fully human?
That is my take.
I don't doubt he was a powerful faith healer but that is not necessarily a supernatural act.
When were the books of the NT written down? Long after he died. The stories of his life circulated orally for decades and, like the game of telephone, each teller would add his own emphasis, theology, and mistakes. As I've said before, conspiracies are organized so this was not a conspiracy, just a case of theology being more important than historical fact. There are numerous instances of scribes changing the texts they transcribed, sometimes by accident, sometimes on purpose. If you can't admit that to yourself you are being willfully blinded by your faith.