Clown tangs can be huge a holes so I'd definitely make it the last fish. You could do a shoal of anthias with the fish you are adding as well as some smaller rock dwelling fish and no tanks complete without a wrasse or 2
20 Gallon SPS reef
29 Gallon FW "fat catfish" tank
20 Gallon Long Dart Frogs "Zig" and "Zag"