Tank is a touch on the small side for a large group.
Ideally you'd want to be looking at 125 US Gal (4x2x2 foot) for a group of 6. in your tank, you'd be maxed out at about 3 fish when grown, and with a group that size, your risking aggression problems.
As for growth rates, its slow compared to most cichlids, but not heart breakingly slow like clown loaches