All these questions are good starting points but it will depend on your ability to digest the material and experiences you'll find on your quest. It's not for us to answer them for you, all we can offer you are opinions, and I don't suppose you'll be ever satisfied with other people's personal truths.
Manoeuvering outside established religions means foregoing the certainty of Truth with a capital t. Such spiritual freedom can drive some people to despair, materialism, or nihilism whenever they read books by true believers proclaiming their own faith to be in sole possession the Ultimate Truth in contradiction to dozens of Ultimate Truths professed by others. Chaos magic has a lot to say about the usefulness of paradigm shifting, adopting a random belief system for a time and then switching to the other, making the mind nice and pliant in the process.
In the strictest sense of the word, truth is a higly exclusionary, binary term, a fact that you mentioned in your post. If one doctrine is true, does that necessarily mean that all others are wrong? In my opinion, thinking in such absolute terms is unhelpful. What is much more rewarding though is searching for wisdom. Correct or incorrect are not the main criteria here, it's a much broader concept. Wisdom can be utter practical know-how (e.g. spiritual techniques), other times deeply empowering philosophies complete with inspiring quotes and including information you've never even dreamed of.
Over time, book wisdom will rub off on you, and you won't even ask the same questions as you did in the beginning of your quest. People may call themselves searchers after the truth but I think what they really do is looking for wisdom.