I have 30 fish in my 55 gallon tank - I know it sounds like a bit much, but here's what I have...
8 juvie yellow labs (2 inches each now, should get about 5 inches as adults)
15 juvie demasoni (1 inch each now - should get 3 or so inches as adults)
7 juvie acei (1.5 inches each now, should get 5 inches as adults)
None of these fish are over 2 inches long right now... plus I have two filters, but will be adding a nicer filter as the fish start getting larger... I'm new to cichlids, but I'm going on the advice, that if the tank is over populated, the aggression is dispersed - so far so good... Maybe these fish will live forever, but I'm also going on the assumption that they won't all make it until maturity... from what I can tell, the cichlids I have seem pretty hearty...
I have other tanks around the house, so if aggession becomes an issue, I could always swap the 55 out for a 75 and keep the same stock list, or divide them up.
As far as advice for you, freddy, I'd narrow it down to fewer species... but that's just my opinion... I've always liked keeping groups of the same species together, but I know many people have very beautiful mixed cichlid tanks... especially mixed male only tanks.