choc. ship stars as mentiond will eat any corals you have, any clams, any inverts if they can catch them etc.
they will be very active when looking for food but when eating less active.
you can feed them anythign from shrimp, clams, squidd, octo, saltwater fish such as silversides etc. etc. they will also extend their arms at the top of the tank to try and catch some flake food or seaweed.. this is what i feed all of my predatory stars
you should have floated the star for about two hours then drip acclimated the star for about another 2 hours, but its too late now and hopefully will be fine.
the tank is also way too new for a starfish at only 5 months, but once again its too late now and hopefully it will be alright