I'm reading "Jesus and Yahweh - The Names Divine" by Harold Bloom and it asks a lot of these same questions. Some may never be answered. We might be stuck with a New Testament with a nameless author(s). It's an interesting study, to be sure, to try to find out where the material came from and investigate clues to determine who, what, where, why. But only if there's no hockey game on and in 20 minutes there will be.
Seriously, I believe there was a source "gospel", call it Q or whatever. And synoptic authors borrowed from each other. But in 100 years I'm pretty sure fundy beliefs will be gone, and if the human race is still here it might be on its way out too. We live in a precious time in history. Let's not blow it by worrying too much about some fictional "be good go to paradise" book. Of course the Bible isn't alone in that category. Just see it for what it is -- myth designed (?) to teach some lessons and yes, it's perfectly okay to pick and choose what you want, like Navigator here, or like AA and his complete disbelief.