Any fish that can fit a shrimp into it's mouth will try to if given the opportunity. Some fish have smaller mouths and could only go after baby shrimp but some fish like swordtails would be able to eat an adult shrimp when it molts. I wouldn't recommend any shrimp for that tank because of the swordtails and bettas among others.
RCS are one of the easiest shrimp to keep and breed. Basically if you have a male and a female of proper maturity you should have babies in 4-5 weeks. They prefer water temps between low 60's-low 80's for breeding but can survive in slightly warmer than freezing water but they generally stop breeding when the water gets into the mid 50's or so.
They prefer an lakaline pH but can live in a slightly acidic environment, though breeding may cease. Also their lifespans may be drastically reduced if kept in too low of a pH. Harder water is preferred as well by these shrimp.
They will eat uneatern fish food, algae, and they will spend most of their lives picking at "biofilm" from surfaces of plants and sifting through debris on the bottom of the tank. You could feed the tank once every week and they'd do well.
If you decide to give them a try I highly recommend at least a 10g tank soley for them or other types of shrimp and inverts. You can keep as many as 300 in a 10g tank since their impact on the bioload of the tank is so minimal.
