imo convicts are a pain, and guppies are extremely prone to disease. i dont think ud be able to feed ur ray just cherries or any other food that u breed, theyre more of a snack. as for telling apart male and female cherries, males are usualy smaller and females develop a "saddle" on their back which are the eggs in their ovaries. if your interested in reading more bout them, here u go
http://planetinverts.com/Red Cherry Shrimp.html
http://planetinverts.com/Red Cherry Shrimp.html