You can put a few fish in your tank probably start with electric yellows, and maybe a pair of peacocks or something, then maybe mix one species of zebra in there. Maybe 8-10 adults max (start of with more and thin out any ugly ones or excess males to get the ratio you require) Stay away from more aggressive or larger fish like giraffes johanni auratus etc.
And I dont think carbon is needed in any tank I certainly dont use it in any of our tanks (unless im removing anything) and haven't had any problems. As for PH I guess it pays to keep it above 7 but as long as the fish are happy growing and breeding I guess it doesn't matter. I had the PH drop on a tank once with africans and they all sat around not happy at all until I raised the PH again and they were sweet. All of our tanks have coral sand in them either as substrate or in a stocking in the tank or filter just to buffer the water so the PH doesn't change too much.
Good luck alot of people seem to be changing to africans so its good