Bump that up to a 55, and get some pictus cats. Then choose a couple small plecos ( BN's, bulldogs, clowns, ect.) I'd stay away from Otos, they're way too shy IMO.
Check out Hoplo cats. I have four 4" Hoplosternum magdalenae in a 65 gallon and they are a treat. They are extremely active. Constantly sifting through the sand. They come up and eat pellet right out of my hand. I do have to watch because they will spit water out of the tank. They aren't the prettiest in the world but they do have a pretty awesome personality.