some can be mixed with certain mbuna , altho tbh its probably best sticking with 1 or the other in most cases. imo you would be better off increasing the numbers of the species you already have
nice tank! what is the current fish stock you have? acei are good as hold high in the tank!
also get a background for the tank even a single colour one it will improve the colour of your fish by making them more secure! i have a 1000 a good tank but upgraded the filter to an fx5 added a powerhead and internal fluval 4plus