nice start !
considering your mix I would add labidochromis caereulus, pseodotropheus socolofi, iodotropheus sperengae, pseudotropheus acei (I prefer the white tailed variety)
A ratio of 1 male to 3/4 females of those would be very colourful and they are amongst the most docile mbuna, which would be nice for your tangs.
You could probably have some more peacocks as well in that size tank. If you did that I'd have no females, but no similar looking males/males of the same species.
You do need way more rock work though. Those carved rocks look good, and are not bad as such in your tank, but you need some large piles, stacked right up to the water line, of actual caves. You can use almost any rock - tuffa is great; light and easy to arrange - you don't need that spendy stuff.