Re: the theory discussion... it's fundamentally impossible to write music without knowing theory to at least some degree. Even if that's just "if I play several downstrummed palm-muted open power chords, then one on the first fret, then one on the third fret, it sounds heavy" -- congrats, if you know that, you know some music theory. You have observed the results of creating sounds out of your instrument in one way in such a way that you can apply those results elsewhere -- that's "theory" by definition.
Once you play your first caveman chugs, you know theory, and moreover, you're actively using it by continuing to play the sickest, most ignorant, most filthy and wrong riffs you can manage.