Why are you still looking to add? :-? Or do you think that 15 cichlids, 3 bottom feeders plus dithers, is somehow not enough fish? :lol:
An oscar becomes a very large fish, usually sooner rather then later. A green terror can eventually become a very large fish, and IME as a large adult is a serious bully, picking on pretty much anything it can. Regular pleco ---again a large fish. A blue acara, port acara and JD all can get 8" or more ---all good sized fishes. Male cons---- a very bulky 6". Mbuna --5-6" and at times rediculously aggressive.
You have a mix of fishes of very different temperments. An odd mix from most people's perspective. All fairly recent purchases and all still juvies, for the most part. See how things work out for a while. And consider, over time, possibly removing something .... not "what more can I add, what more can I add".