You may want to read up on this but copper and clown fish I do not think mix very well? I know puffer fish are ich magnets, I am not sure about cowfish? Damsels can be a pain in an aquarium because of there ability to pick on other fish causing stress. Sounds like you you have cured the ich problem in your tank but that it keeps coming back? If so one or more of the fish are getting stressed or has a poor immune system. It can take months for an aquarium to go dormant once there are no host for ich to attack. The 29 should be plenty large for your other fish lf you go with copper. I wish I had a better answer maybe someone else can do a better job.