The main problem with this sort of tank size will be aggression. If you have a group with one male and 2 or 3 females your have very few if any problems two males in a tank that size will give you problems once they reach sexual maturity.
Plenty of caves and hiding places may help.
I keep the smaller Hypans (201and 411) in 18" x18" x 18" tanks with no problems.
One thing that can help is making the caves with "Line of sight definers" that is some thing the fish can see know the cave is "his"
As Mr G has said water quality and good housekeeping are a must, don't go along this road if you cant do regular water changes and small target feeding.
Regards Bob