In a 30 gal.. I like the combo of Senegals with Ctenopoma (leaf fish) and they do not fin nip like previously stated. Senegals might be a little big for your tank though, plus when they do get bigger I'd be afraid for your little (4/5") pleco. Loaches are always a nice addition. I have housed multiple (4) peacock eels before and find they become quite active. Firemouths- depends on personality, I think they are quite peaceful (for a cichlid, but definitely would not house them with leaf fish- tried that, ended up separating them. Knifefish are great too, but alot of the available ones get big (Black Ghost), but the African Brown should be good.