Honestly it is not that difficult, the key is to get a large number to spread aggression and get ones that are in the size range. Also take your own advice and keep just peacocks and haps, I see several people mixing them with mbuna, victorians, tanganyikans. While some people report great success, I have also seen the damage mbuna can do because they have actual teeth. Predator Haps would also be something to avoid unless you have a bigger tank to separate them into later on as they grow much bigger than your average peacock and small species of Haps. I use to keep large rocks and structures to offer hiding spots, but found that it increased aggression. Some of the "tank bosses" would become territorial and attack any cichlid that came near their "spot". Aggression has gone way down since I removed structures. I just have my Universal Rocks 3D background and sand now.