You could get a whip tail cat. Theyre oddballs. I got a jaguar catfish in my oddball tank. Buts he's pretty boring thank fully he lives in a clear tube. But they look awsome
Banjo catfish, Leopard Ctenopoma, Butis Butis, African butterfly(although my old BGK was a suspect in the murder of one of African Butterfly's) yellow tailed eel
spiny Eel of some kind? Catfish you could have Raphael? I would suggest maybe having some Loaches of some kind in there. there are a lot of cool smaller to medium sized loaches that would do well in your tank. I like that you have one eyed fish. I myself have a 1 eyed oscar and a 1 eyed clown knife
I would advise against getting an elephant nose, they have electric organ on their body that allows them to perceive the world around them and anything that moves. its how they hunt. BGK's also have this organ and keeping more than one fish with the organ in a tank together will cause them confusion and distress. Although elephantnoses seem to be okay in groups I know that you aren't supposed to mix them with BGK for that reason.
About Sun Catfish, they can be pretty mean. I own three of them and together they have taken down 4 3'' gold fish. and they are only around 4, maybe five inches long