A: Age, ability, experience, instrument of choice, and requests (e.g. to be with a friend, or with or separate from a sibling). We do not guarantee that every student will be in a band with others of exactly their own age. In fact we find an age range beneficial; a 2 to 3 year age span within a band is normal.
There tends to be one drummer, one bassist, between one and three guitarists, and optionally one or two keyboardists. Multiple vocalists is common and encouraged.