Hey there friend before i would worry about what else to stock with i would slow down and look first at what you have already. Forget the knife fish let alone the elephant nose, think about how big your black shark is going to be and act like when full grown. which is around 2ft long!
Its always fun and easy for us hobbist to get excited when wanting to add new fish to our tanks. i know im a kid in a candy store that way to. But you have to realize the if your not getting rid of fish and are just going to add fish you then have to consider they all need there own space and territory to co-exist peacefully.
tonyro