Did I play this Czech Benoni correctly?

Hello. I'm seeking feedback on my play during this game and wondering if I understood this opening or not. I'm playing as Black.

Things I understand are that Black's dark-squared Bishop is the weakest piece on the board. It's a bad bishop and would like to be traded as early as possible. Black's d6 pawn is the root of his defense and it should be protected at all times, everything falls apart should it be taken by an infiltrating Knight. d6-e5 pawn blockade is similar to the King's Indian Defense and means an f5 pawnbreak may be possible. There is an almost zero percent chance Black will get checkmated due to how slow and closed this opening is, so always expect to go into the endgame.

Things I don't understand: Why does Black's b8 Knight go to a6? I've read Black's Queenside pawnbreak is b5. You will prepare this with a combination from Na6-c2, Rb8, a6, and/or Bd7. What is the point of the Queenside pawnbreak? Is it to open the b-file? Or not necessarily?