Temps of 70-80F are fine, they are not picky. Keep them well-fed but don't pollute the water, and you will have more shrimp than you need. When all their food is gone, feed them again, check twice per day. They breed fast, like mice. Or guppies.
I raise RCS for the local pet store and sell them on ebay. I got the shrimp in Mar 2006. After 3 months I had so many I had to get another 10g tank. Now I have 3 10g tanks FULL of RCS. Unfortunately I don't have any fish to feed the RCS to. Maybe I should get a catfish...