Wing Attack is a brilliant move for Zubat. It is it's first Flying STAB move, and it won't get too much better than 60 BP for a while. I suggest replacing Astonish. It's astonishingly (geddit?) weak, and the Supersonic can be really clutch sometimes. Leech Life is good coverage, but weak in Gen 3, being 20 BP. Bite is okay, but that can be replaced with a Poison STAB move later maybe, but it's not terrible.
I would say, get rid of Bite or Astonish. Astonish is literally so weak, and Bite would be good, if it wasn't still Special in this Gen...
So yeah, get rid of Astonish or Bite for some STAB Flying/Poison moves. The only move really worth keeping is Supersonic, but otherwise the rest of the moves are okay until it gets better ones.
Good luck with the playthrough!