Yes
yes, rather easily.
not a good food source. Marine animals and Freshwater animals have different evolutions and as a result they aren't constituted the same. As a result they also have different nutritional needs and one will not live well on the flesh of the other. The fatty conposition of freshwater animals will cause liver diesase in marine animals. Best bet is to feed things like Krill, Silversides, saltwater mussels, and other marine feeds. So setting up a breeding colony of freshater snails is not the way to feed a mantis shrimp.