not sure but MAYBE cleaner shrimp are territorial. also, you could do a mantis... but nothing else would be able to go in the tank. and the wally world starter kits should be fine, but i wouldnt put the media in the filter. maybe you could block it with some eggcrate and put chaeto in there to help with nitrates. since you wont be doing corals, the lighting will also be fine. goby and a firefish seem fine btw. just to warn you though, firefish are super shy.
oh yeah, he posted just before i did while i was typing. sometimes gobies and pistols form symbiotic relationships, so that seems pretty cool.