Even a baby ball python can eat a pinky rat. Gerbils could work, but they don't get nearly as big (or grow as fast) as rats do. I don't think they reproduce as quickly either.

For my mice/rats I keep the male with the females all the time. You can't just put the male in and take him out all the time.. you're begging for the female to kill him. Mice kill strangers, and one that is gone for a week and suddenly comes back can be considered a stranger! Talking from personal experience here..

I feed high quality dog food (Nutro brand Lite variety) with a mix of puffed rice/wheat oats, cheerios, and tri-color pasta.

The whack method of killing is not very efficient or humane. I use carbon dioxide to kill mine. Do a search for co2 chambers and you should come up with some threads on making the chamber.