BrianH is right, featherdusters are filter feeders and once your tank is established, you will only have to occasionally feed them DT's (an excellent product that you can buy at some LFS, it must be kept cold...and ALL filter feeders will like this). I have several dusters that I've had since I first started SW, they are a little over 2yrs with me, and I feed only once a week. BTW, damsels won't harm dusters at all. Hermit crabs are good, but go with the small blue legged hermits. They tend to be hardier, and they also don't have the reputation of sometimes bothering other inverts. Don't forget snails. Personally I like the astreas, I also have some keyhole limpets that do well, but they have the drawback of eating clams, and scallops so if you plan on keeping mollusks, then forget it. Turbos are okay. It all depends with them. To me at least, they are clumsy snails that will eat some of your best macro algae.
Considering the size of your tank and the fish you already have, I'd go with one of the larger clowns. Tomato or maroon are very nice and have excellent color that would be a nice off set to what you already have in that tank. Plus they are quite able to take care of themselves with regards to the damsels.