I would not mix mbuna with the Aulonocara species.

They are too fragile and will not last too long. As for Haps. This depends on which ones you mix with the mbuna.
I have 2 Placidochromis milomo and 1 Placidochromis johnstoni solo in with my mbuna. No trouble with them. The solo was quite small when introduced and has grown quite nicely and is now bigger than most of the mbuna.
As for numbers of mbuna, you have a choice. I personally don't like too few fish in a tank. Watched a Nature program the other day and ther was a bit on Lake Malawi. The fish density is quite amazing. Showed us a Tyrannochromis mactrostoma female with her fry and how they swim in and out of her mouth. Quite something to watch.
My tank density does not resemble what you see in the lake and I have around 40 fish in a tank a little smaller than the tank you have. It just means a little extra cleaning and regular 20% water changes, weekly.
Have a couple of 3ft tanks which are running at about the same density level, all my fish are wild caughts, and have had 5 females start to carry in the last 24hrs. Am presently carrying around 300 F1's, 8 different species, at the moment. My Ps. galareya long pelvics are spitting out between 45-55 fry at a time.
A tank with too few fish looks empty to me.
