Africans will push the 3 foot mark, but more importantly this is a very specialized feeder.
They are filter feeders so you will have to supply foods like plankton, live worms, insects, fish, and shrimp. I've never really heard of Heterotis niloticus accepting prepared foods with great success.
Personally, I wouldn't keep an African with those other tankmates...I would say you would be better off with a silver or black considering those are possibilities for you.