I think he is asking whether 30 fishes in his tank is over crowding?... anyway i feel that as long as your filter can handle the bioload it shoud be ok. Check your water parameters regularly if u want to be on the safe side.
Depends on the fish size...I ever kept 50 neon fishes in 2 feet planted tank...
no problem as long as you have good filtration and regular water change (once a week) for 20% of the tank.