How do I feed a sourdough starter?
When I've made and used starters in the past I've generally fed it 1/2 cup water and 1/2 cup flour every other day.  The challenge with sourdough starters is that you need to be using them regularly as the volume obviously grows if you're just feeding it and not using it regularly.  Of course a friend, family member, or neighbor might be thrilled for you to share it with them but then again...it's kind of like having a pet - you have to keep it fed!