9. O-O-O??

I've tried to annotate this because there were some pretty glaring mistakes i think i found, i'm just wondering if there are others I made. Figure since I won it should go in this topic. Hope that's OK.

9...Bg7 only serves to clear a path for castling, but
9...Bh6+ does the same and gains tempo.
white's only playable escapes from check, 10.Kb1 and 10.Nd2, are non-developmental.

will do my best for insights.

3. ... a6, normally a tempo loss
White often plays 4. d4 breaking the centre vs a sicillian, in this game he's locks his white bishop out of play :/

7. Bxf6? Qxf6! White trades his strong bishop for a pinned knight
Black recaptures correctly. 

9. 0-0-0 ? Your right, better would be just Rd8 instead of castling into the firing line.

11. ... 0-0
Pushing is better, whites centre-breakthrough preparation is inferior to your kingside attack by at least a tempo, if I was white i'd be willing to sacrifice my e-pawn via Rhe1 to stop your momentum.

12. Ng1? (not Rhe1) a5!
Black threatens a6 winning the bishop for a pawn (creates a semi-open activating the rook)

13. a4 (is better than a3 for sure)

15-18 white escapes in the wrong direction. Your moves look sound to me.

19. ... Rb4? (Rb6) the reason becomes evident 2 moves later.

20. Nxe2 was better than Nxc2 after 21. Rdb1 (also given that a depth analysis reveals it's a free knight)

21. c3? (lose the bishop or be mated) much better is Rdb1 (but allows you to save your knight)... this is still the preferable move for white, since his bishop is doing a more important job than your knight now.

21. ... Rb6 is better! - (White cannot defend against mate threats / save the bishop & take the e2-knight)