Therefore, if God does exist, it's not worthy of my attention.
That's really enough to know. I am way past "IF God does exist" but any negative cannot be absolutely proven, so your thought is sufficient.
Jesus could have been invented out of thin air or exaggerated from a real person. It matters not.
I believe Paul's Christianity would have been similar to Buddhism- accept what you want, reject any of the myths if you must, accept that the overall goal is goodness. But something happened along the way, perhaps at the First Council of Nicea. Christianity became a "state" religion and became a force for no good. When people want to argue anything about Jesus or Christianity, we can always fall back on "Therefore, if God does exist, it's not worthy of my attention."
I like your thoughts on being responsible for ourselves and our morals being above that of the gods.
"Sin" is an invention of religion. Sin is addressed by appeasing the religion by some kind of sacrifice (typically- money) There are things that are right and wrong, moral and immoral- but you need religion to turn it into sin.