How Much to Feed and How Often?

[eeyipes]

Greetings all ... new to snake care here. The kids caught a Western Terrestrial garter snake a few days ago and want to keep it a few weeks, and then release it and catch another, and so forth. We've set up a 10 gallon with a water dish, log hide, and some climbing items. Our first garter seems to have settled in good. We've fed him 2 rosy minnows and an earthworm in the past 2 days. Is this about the right amount to feed him? How often should we feed him? He is about 18" long. Thanks!