One thing you could try with the lombardo's (Kenyi)is having reverse trio's or 2 to 3 pairs. this helps spread the aggression between males, plus this means the females will not get the constant harassment from males. With some species it works and others it doesn't, its all about trying multiple options until you get the right stock for your tank. At the moment it seems your tank is settled as james said but if you do want to add to your current stock list then id do so when it comes to changing over tanks. The Pseudo Crabo id try and re home as these do get quite large and if its a male he may suddenly change his attitude in the new tank. Id also thin out the zebra's as ideally you dont want the offspring to be interbreeding with one another. As for mixing I personally think keeping mbuna with mbuna is best and vise versa with the peacocks. With the 75G you could have 1 to 3 species of peacock (max) as these need the extra swimming space (as you may know) plus the mbuna need the space to thrive well to, I wouldn't pack it full with rock either, just some nicer large pieces with scattered medium to small species at the base. The main thing is to brake the line of sight and if you watch your mbuna (I know with mine) a lot of the time they are in the open areas, they do go in the rocks but spend most of their time grazing the algae and just chilling out above their rocks while doing a little digging.
Just remember that the mbuna can be very boisterous fish so the peacocks may not colour up to their full potential.