Uh, welcome to the boards.

Interesting that you should bring up the “pagan parallels.” I’ve been researching the alleged pagan parallels recently, and they’ve all been either highly suspect or totally fabricated. For instance, the legends surrounding Alexander’s virgin birth are commonly cited by detractors such as yourself, but they don’t realize that those legends arose three-hundred years after the Gospels. Christianity became so popular that pagan “religions” copied Christianity, not the other way around. And such facts are present in nearly all of the alleged pagan parallels. The popular claims from detractors about Mithra and Egyptian mythology are all pretty much bunk.
And “only sometimes” supported by history? You’ll have to go into a deeper discussion on that because studies I’ve read have shown the remarkable historical accuracy of the Bible. For example, for centuries, many of the tribes and peoples talked about in the Bible were unknown to historians and considered them to be fiction until archeologists unearthed conclusive evidence. The Hittites are an example I’ve been reading up on.
And, yeah, you can say that some or a lot of what is written in scripture was written after the fact… but such has been the case of all historical ancient documents. What comes to us about Socrates, for example, was written hundreds and hundreds of years after he died by people who never knew him. What comes to us about Jesus, however, was written only 20-60 years after he rose to Heaven, which is remarkably close for ancient history and speaks to just how significant this figure’s life was.
The different number of books isn’t really too troublesome, it’s more of a theological difference more than a problem that has to do with believing their content.
Speaking for myself, direct experience and intuition along with modern miracles from Heaven have corroborated the truth of the Christian story and have helped me become more confident.