Hmmm, in all honesty it is far to early to be adding any filter feeders such as feather dusters, otherwise you will need to use food for filter feeders, of which there are lot available, BUT doing so you run the risk of introducing too much food/nutrients in the water, especially for a new tank.
The brittle/serpent stars are rather easy to feed, just put some meaty morsels of clam, fish, etc, in there next to them and they will eat it.
I have a green brittle star and he eats anything and everything I put in there, flake, brine shrimp, Mysis shrimp, etc. Before long they will jump into action as soon as they smell food in the tank, and boy those suckers can move fast!
He is actually the most aggressive critter in my tank right now and has even attempted to eat a hermit crab, without mush success. LOL
crabs and shrimp are easy to feed as well.