You could probably do a couple more of the peacocks and the yellow labs, and that's about it. I would stay away from the crabro, common name bumblebee, as they get quite large, 8+ inches, they are alos quite aggressive. Demasoni stay small, but are super aggressive and usually have to kept in groups of 15 or so to spread the aggression out. Frontosa are a definate NO... they are a rather mellow and mild mannered fish and they like to kept in groups of their own. most likely juvenile fronts won't make it very long with mbuna, mbuna are just too aggressive. Other reasons that you can't put fronts in there, the tanks is way too small... and if fronts were to reach adult size, your mbuna would be a yummy lunch for them.
So... I'd just think about adding more peacocks and labs. keep in mind that they're dietary needs are different as well. I'm thinking maybe 3-4 of each, trying to keep the ratio at all males or 1m/3-4f. HTH