Ghost shrimp are easy to feed. Repashy is amazing stuff but it is expensive ! I feed mine shrimp pellets, algae pellets, [sinking kinds] and they will also take fish flakes and anything else they find. A special diet is not needed, they are scavengers and do very well as scavengers. Unless a tank is practically sterile, they will have plenty to eat.
Mine particularly seem to enjoy shrimp pellets, squicky as that seems.. they will eat each other if one dies, so I guess it makes sense.
So long as you have reasonably hard water they don't need special calcium, they eat their moulted shells, as do most shrimps. But you cann put a bit of a calcium pill in if you feel the need, or a piece of one of those vacation fish feeding blocks, which are mostly calcium,and if they need it they'll pick at it.