you will prolly need to feed the shrimp a star a week. the best thing to do is find somebody with the tiny algae eating stars and get a couple of them from them. let them start to take over your system than get the shrimp. if done right the shrimp and the stars will reach an equalibrium and you will not need to buy more stars for the shrimp to eat.
They will eat sandsifters as well. They take those paddle looking pinchers and "scoop" sand out to get the sand sifters. I watched my pair pull a sandsifter out that was 10 times their size and drag it up the rock. The aslo eat the Asteria stars. i had an infestation of those and they decimated them.