If thats what you want than go for it dude, just pay close attention to them later down the road for any one not fitting in with too much aggression being applied to a certain species..
With the trets if you have a few in there they may keep to themselves with aggression sorry i forgot to tell you this the last time..
The Haps and Aulonocara should focus on each other as well.. Well til something decides to breed than thats where the rock heavy comes into play, just rock out this tank and the sand sounds sweet but you may want to lay some egg crate on the bottom to help with the load of rock..
Good luck my friend..