Reversed Sicilian - What's wrong with my plan? I played this game in a tournament and lost.

[fen ""]
[StartFlipped "1"]

1.c4 e5 {Starting the reversed sicilian} 2.Nc3 Nc6 3.g3 g6 4.Bg2 Bg7 5.d3 d6 6. Nf3 Nge7 7. O-O O-O 8. Rb1 h6 {Finished the Closed Sicilian setup that I want: h6, Nc6, Ne7, O-O, Bg7, g6, and the d6-e5 pawn chain. This is the exact reverse of Karpov's Closed Sicilian when he is white} 9. b4 {I always want this move by my opponent when playing the Closed Sicilian because his Knight can be a target, but I also needed to oppose his queenside plan, though I was not really sure how to do that. I was thinking that I should try to close the queenside so that I can focus on my attack on the kingside} a6 {I couldn't think of any good way to frustrate his queenside attack, so I played this move because I have seen this in some Karpov's games, but I don't really know its purpose, I just "hope" that I can close the queenside in the future with this move} 10. a4 f5 {Started to attack his unsupported Knight} 11. b5 axb5 12. axb5 Nb8 {I did not know where to put my Knight, but I was thinking that the c5 square will be a good outpost for my Knight, so I retreated to b8} 13. Qb3 Be6 {The purpose of this move is to prevent a possible discovered check} 14. Nd2 Nd7 {Preparing to post my knight to the c5 square, so my b-pawn can't be taken because of the fork threat} 15. Ba3 Rb8 16. Na4 b6 {Closing the queenside at last} 17. Nc3 f4 {Starting my attack on the kingside. My plan is to post a Knight to d4 via the f5 square, then after posting the Knight to the d4 square, I was thinking of attacking the f3 and the e2 squares} 18. Nde4 Nf5 19. Qc2 Nd4 20. Qd1 Nf6 {Vacating the d7 square for my Queen, I was also thinking about removing my opponent's light-squared Bishop to help my attack on the f3 and the e2 squares} 21. Nxf6 Qxf6 22. Nd5 Bxd5 {Now my time trouble has started. I was thinking about putting my queen to Qf7, but after that, there was nothing that I could do to remove his Knight. Then I thought that by simplifying things, I can win a pawn by playing Nc2 at move 27, yes I calculated that, but unfortunately it was a blunder.} 23. Bxd5+ Kh7 24. e3 fxe3 25. fxe3 Qxf1 26. Qxf1 Rxf1 27. Kxf1 Nc2??? {I thought I could win a pawn here that's why I started simplifying things starting from move 22, so I played this move very quick, and immediately after playing this move I realized that I already lost the game} 28. Bc1 e4 29. Bxe4 d5 30. cxd5 h5 31. Ke2 Bf8 32. Bb2 Na3 33. Rf1 Nxb5 34. Rf7+ Kg8 35. Bxg6 Ra8 36. Be5 1-0


I have added comments at the following moves:
1, 8, 9, 10, 12, 13, 14, 16, 17, 20, 22, and 27

I don't really understand how to handle the pawn structures at the queenside.

Is there something wrong with my plans, my thinking process?

My opponent claimed that he was winning the middle game, but I think he was wrong, I think I was winning the middle game here. Am I wrong?

Thanks!
8. ... h6 was unprovoked. Until White threatens to double Q+B on a c1-h6 diagonal, or places the piece ag g5, there is no reason to weaken the Kingside. The plan calls for immediate 8. ... f5, e.g. 8... f5 9. Bg5 h6 10. Bh4, and it is up to Black to decide between 10. ... g5 and 10. ... Bf6, whichever suites your style.

Along the same lines 9. ... a6 seems off. Black shouldn't help White in opening Queenside files. If you want to secure Queenside, 8. ... a5 is in order of the day.
Did you consider 12. ... e4?