One Big Zonatus or Argentea would be cool. Maculicauda or Oreochromis tanganicae ( whoops not a CA but still great choice) is Fanastic center piece just watchout they get huge about Dovii size.
A male Green Terror would be the best fish for what you're describing and usually has plenty of attitude when you put them in a small tank like that. They get very interactive with their owners.