I would like to receive some feedback on my mistakes of the below Lichess game, if possible from someone above 2000. I an unsure about the reason of the mistakes I did in the game. When I finished the game I thought I had won quite convincingly, but apparently, I made some mistakes early in the game. I was playing with the black pieces.
[Title "ulimilu1997-bird67, lichess.com, 10/11/19"] [FEN ""] 1. Nf3 Nf6 2. Nc3 c5 3. g3 d5 4. d4 cxd4 5. Nxd4 e5 6. Nf3 Nc6 7. Bg5 e4 8. Nd4 h6 9. Bxf6 Qxf6 10. Nxc6 bxc6 11. e3 Bb4 12. Qd2 O-O 13. a3 Bxc3 14. bxc3 Qf3 15. Rg1 Rb8 16. Be2 Qf6 17. Kf1 Bh3+ 18. Ke1 Rb2 19. a4 Rfb8 20. Rc1 Rb1 21. Kd1 Qxf2 22. Qe1 Qxe3 23. Bh5 Rxc1#
I played 7... e4. Later, I realized that d4 was probably better but I get the feeling that after 7... d4 8. Ne4 Be7, Black has lost some initiative.
I played 8.. h6 as White’s Bishop is forced to be exchanged on f6 or to retreat to a passive position. I calculated 9. Bxf6 Qxf6 10. Nxc6 bxc6 with a more or less favorable position in which the powerful center, which will be stronger after c5, is an advantage for Black. However, Stockfish evaluation drops around 1.
I played Bb4 threatening to win a pawn. However, it is considered a blunder. I do not understand this. I do see that 12.Qd4 forces the Queen trades, but to me, the position is not much worse for Black for it.
Given that the g3 pawn of my opponent is on a dark square, I thought of trading the bishop. I now realize that maybe this bishop had some prospects on the g1-a7 diagonal, but again I am not sure why this qualifies as a grave mistake.
Note: If possible, could you please also tell what move number you would stop at in order to calculate variations? I am unsure if I am doing this at all, but all my calculations take only 6 moves at best by each side. I know that in the middlegame, I should probably do some analysis of variants but in games I am not sure how deep these analysis should be.