Thanks for your feedback!
I wasn't sure what would be the best default range as I didn't want it go get too long after some upgrades. As for health drops, now that I think of it, it would have perhaps worked better to always have health drop after a few enemy kills instead of them dropping randomly. Pretty much only the first area was tested properly so the enemy placements in other areas are sometimes off.
Yep I tried to come up with a good attack sfx that wouldn't become irritating but didn't manage to do that.