I don't think you have to much to worry about. I have a 55 gallon that has 1 med. naso tang (Big Boy) I just love him, 1 yellow tang (Guber), 1 foxface fish (Foxy Roxy), 3 bubbletip anemones, 1 small tomatoe clown, 1 large tomatoe clown, 1 spotted hawk fish (Hawk), and 2 fire fish that do nothing but hide in the cave (woody and boner), and 20 pounds of live rock. I have had this for sometime now at least a year. Although funny you posted about damsel fish today, because today I took out my 2 jewels, 2 devil blues, and 2 black neon velvets, that were just a pain to my other fish. I have an excellent store here in town where they have been owned and operated for over 4o years. They told me today never to get damsles that they will become unwanted. If you would like some small fish I suggest something small like a tomatoe and anemone, you would just love this combo in your tank.