...With such diversity, it would be interesting to know what Christianity itself teaches.
I think what you mean is, it’d be interesting to see what Jesus himself taught. I have a feeling most Christians would be very surprised! They’d also be surprised to see him in person.
My understanding of the latest historical research is that there was no one version of Christianity to start with. This seems to be leading to stronger proof that there was no one person named Jesus. It was either stories adapted from other legends and told by a group of people then jelled into the early gospels, or a story that kept getting retold and modified. Either of these fit better with how stories were told at the time, as opposed to any kind of historical documentation that could have gone on. There is ample evidence for a variety of small Christian cults with differing beliefs during the first and second century.
I’ve never quite understood how the theories are supported of exactly when the original works were written down. I know the earliest manuscripts we still have are mid 3rd century, but somehow they can date the originals. For me, this early history became less and less important as I learned more about it. The Christianity we know today is based on Byzantine versions and strengthened later by the crusades. This is the opposite of what peaceful Christians today want you to believe, but to me, if it wasn’t for the militaristic, King supported version of Christianity it would be a footnote in history like zorastrianism.
Most historian have accepted Jesus as a historical person.
Prof Bart Ehrman has discussed this here