No matter what size tank you have, someone else has one bigger, lol.
I'd be torn on what to stock it with. Part of me would want to do an african cichlid reef. If money were to no object, then a saltwater reef. And then another part of me thinks a bunch of "small fish" would be a waste of such a HUGE tank and instead would get some aros (and then probably some bigger catfish for the lower level of the tank).