I wouldn't put cichlids in a 30 gallon tank, but you could put a good amount of tetras, rasboras, dwarf guaramis, and other small peacefull fish in there.
Also, i would at least consider a saltwater tank. If you do a fish only tank, it is basically the same keep up except you need to keep an eye on the salinity. Other than that, it is very similar to the upkeep of a freshwater tank. And the is a greater variety of fish to choose from
100 gallon reef
50 gallon FOWLR aggressive
80 gallon discus tank
135 gallon fresh community tank