As center pieces you could get 2-3 individuals of one of the African Bathybates species, euther leo, horni, or Graueri. They get between 10 and 12" long. The leo and horni pics are by Konig, and the graueri pic is by A.D. Mohamed.
I have a few Krussie. I know they get about a foot long but they are not to mean and look really neat. so a pair of those and some clown loachs would be ok. then you would have fish eaters that are rare and not so mean you have to keep them all alone.