Keep predators away from them and that is about it.
The starfish will fend for themselves, although you may not see much of them. I've got them in my refugium (my Tobies pick 'em off in the main tank) and once they find a nice safe place to live you don't really see much of them.
From the advice I've seen online the same should be true of the tube worms/feather dusters. I've had plenty of stores insist that they require phytoplankton, but haven't kept them yet so I can't say for sure if that is true or simply a sale pitch. Most the advice seems to be that they'll find their own food though.