They are really small, so having 6 or so in your tank is fine, even if those eventually reproduce. I would get more than 1. They aren't like snails that breed like rabbits.
I would still feed them maybe part of an algae wafer at night....or every other night, but let them get the flakes too.
If you decide against the ghost shrimp, another option would be getting a turkey baster and sucking up the leftover food after you feed. They work really nicely, especially in small tanks.
