Since you have one clown loach already, I'd suggest several more. They are naturally a shoaling fish and tend to be more social and outgoing the more you have.
Filter wise I am still partial to the canisters because it is what I have always used. But I am familiar with sumps. But my clear choice of canister filter is Eheim 2260 or 2262 by far if you have the money.
I had a sump and canister setup before (FX5, 405, and 50 gallon sump on a 110 gallon tank)... So I can mix and match for superior filtration. I will look into the eheims.