I don't want to sound rude, but... welcome to your first existential crisis. I had my first at 12. Not everyone has them and (without trying to sound self-absorbed) it's been my observation that only the brighter and more introspective people experience them. You're not over-analyzing at all... you're just trying to find how you fit into a world that is far from being able to be understood.

You're questioning values and existence. Maybe even considering what it means not to "be." That's implicit in questioning the worthiness of life. You're asking questions that are universal and some theologians and fewer philosophers claim to know the answers. Wikipedia, if I recall, has a good article under "existential crisis."

I've gone from observant Roman Catholic to theist to nihilist within two years so my answer to your questions would be "no" and "nothing." It was far more comforting to believe in something rather than nothing, to believe that life has a purpose, etc., but it was also dishonest and, at my old age, I just couldn't help but come clean.

It's a ridiculously trite and overly pompous phrase used by arrogant blowhards, and a phrase that I think is, wrongly, often appropriated by the Ayn Rand crowd, but I watched Kenneth Branaugh's Hamletagain last year and I think that I would have Polonius' "This above all: to thine own self be true" tattooed on the chest of every newborn. I don't believe that it's a phrase that should be appropriated by individualists, although it has, and I don't believe that it means to think of 'self' "above all" or, for that matter, to really be"above all." Most people drop the "this above all" when using the quotation.

The Beach Boys sang it best:

Be true to your school,
Just like you would to your girl.

Or guy. Whatever floats your boat

Yep. That sums up the meaning of life pretty well.