You are awesome! I wish I could radiate only half as much enthusiasm and happiness. Even though I feel it - I just can't render it as much. I plan to learn from you in this regard!

You are welcome. I will also try to answer your questions. Some of them I ponderd myself and arrived at some answers. But then I had more time. I have a comparable background and I have a deep interest in children so you may also find my ressources for parents of interest.

But now to your questions:

My friends suggested I become a missionary, but to me, it made far more sense to become a high profile lawyer and donate 90% of my salary to fund a dozen other missionaries. (A Christian version of effective altruism?) No one ever understood!

Awesome. But it can be explained by the presence of memes in real-life christian culture that regulate such actions as misguided. See Reason as memetic immune disorder.

Who was the historical Jesus? As a history source, why is the Bible unreliable?

The Jesus Seminar may have answers of the kind you desire. If a historical Jesus can be found by taking the bible as historcal evidence instead of sacred text, then look there. The Jesus Seminar has been heavily criticised (in part legitimately so) but it may provide the counter-balance to your already known facts. See also http://en.wikipedia.org/wiki/Jesus_Seminar

How can I have morality?? Do I just have to rely on intuition? If the whole world relied on reason alone to make decisions, couldn't we rationalize a LOT of things that we intuit as wrong?

Well. What do you mean by "how"? By which social process does moral exist? Or due to which psychological process? The spiritual process apparently is out of business because it is ungrounded. There was a Main post with nice graphs about it that I can't find.

You might also want to replace the question with "why do I think that I have morality?"

Does atheism necessarily lead to nihilism? (I think so, in the grand scheme of things? But the world/our species means something to us, and that's enough, right?)

No. Atheism does remove one set of symbol-behavior-chains in your mind, yes. But a complex mind will most likely lock into another better grounded set of symbol-behavior-chains that is not nihilistic but - depending on your emotional setup - somehow connected to terminal values and acting on that. "symbol-behavior-chains" is my ad-hoc term. Ask if it is unclear.

What about all the really smart people I know and respect, like my sister and Grandma, who have had their share of doubts but ultimately credit their faith to having experienced extraordinary, miraculous answers to prayer? Like obviously, their experiences don't convince ME to believe, but I hate to dismiss them as delusional and call it a wild coincidence...

I feel with you. I have the same challenge. See my first link above. I respect them. I know how complex this migration is. I was free to explore. How can't I not reciprocate. I don't want to manipulate. I just want the best for them. And then extensions of the simulation argument might actually lead you back to theism (as least a bit).

Good luck and cheers!