Firstly, may i suggest getting more oto cats and more hatchet fish, these fish do best in shoals, and therefore should be kept in shoals. Personally, I find you tank to be pretty well stocked, if you get say 3 more hatchets and 3 more oto cats, then you'll more than likely be at the max, mabye even another gold ram... but that's it, I'd say don't add anything and plan for the furture, because your tank will eventually be full of 3-4 3" rams, 2 6" angels, 2-5 1.5" hatchetfish, 2-5 1.5" oto cats, a 5" pleco, a 12" eel and I'm not sure what the catfish's full size is, however if going with your stock, you have 48" of fish in a tank that should house 42"... mind you the 1" per gallon rule can be appiled losly in this situation IMO because you have larger fish (and I bet a 12" eel wouldn't be happy in a 12gallon tank...) Regardless, I suggest not adding fish now that the specs are set out...