If it's for a quarantine, get a bare bones setup. Quarantine tanks should have no substrate or live rock in them (and, of course, no permanent residents). It's a lot better to just get a tank with a heater, a light and a filter.
A 12 gallon tank would be great for (my current setup as well)
-2 False Perculas (will sex themselves)
-Bubble tip anemone
-Peppermint shrimp
-Tuxedo Urchin
-2 Sexy Shrimp
-Some assorted sea snails for algae control