Personally, I would go with a pair of mid sized cichlids such as Firemouths and some sort of predatory surface dweller such as an African butterfly or a golden panchax. I wouldn't really go with anything larger than 6 inches
Honestly with that hight id do a paludarium. But if i was settin it up as a regulartank id do either a pair of firemoiths, salvinis, hrps, etc, some kind of biotope, or an oddball tank ( spiney eel, butterfly fish, etc