October Novel Prep Challenge

For the calendar/prep, I'd say you are overthinking this. No main character could get anywhere without a strong supporting cast. I can think of no books I've read in which the main character did not have cohorts that easily qualified has major characters themselves.

However, for prep, this is simply the chance to pull out one of those important, but not yet fully fleshed out, characters and get to know them a bit better.

Personally, I'm doing a major character. In fact, he's so major, I'm toying with the idea of making him a POV main character as well.