You could do an Asian or South American biotope tank. There's also the micro-fish setup.
If it were a South American biotope, I'd say:
-pair of cichlids, whether it be GBRs, apistos, keyholes, angels, or any other
-a school of tetras, I'd say one that's normal-shaped like cardinals or black neons, and another more square-like, for example bloodfin or bleeding hearts,
-a school of six or so hatchetfish
-six or so cories of your preference
-and perhaps a trio of otos or a BN pleco
If it were an Asian biotope:
-a pair of some of the more docile bettas, ex. betta albarainga, betta cocina,
-a school of harlequin rasboras would look nice,
-some khuli loaches for the bottom,
-a school of cherry barbs,
-and perhaps (though I'm not sure), you could do a SAE, although feel free to correct me on that anyone.
Microfish are small and you can have more, I like them personally.
You could do:
-a school of espei rasboras or chilli rasboras
-a pair of dwarf pencilfish or sparkling gouramis
-a breeding group of endler's livebearers
-and perhaps a lot of inverts
Or you could try the species only tanks. You mentioned mbuna, I think (but don't know for sure) you could do a breeding group of one male to three or four females.
There's also the option for dwarf puffers, you could do around four or five in there provided it's heavily planted.
Just ideas. Good luck!
