Advice - Take the plunge, it's fun
Optimal team size - I prefer 6-8, though the ratio of adults to kids matters a lot (significantly more than just straight up team size). I keep my ratios at 2-3 kids per adult. Much above 8 gets crowded no matter how many adults you have.
Budget details - PM me, I'll email a spreadsheet.
Schedules - Plan on at least 4 hours per week. I usually split that up into two meeting days. As competition approaches (T-4 weeks usually) I give smaller groups of kids the option of extra meeting time to work on robot programs. A highly competitive team that is set on qualifying for competitions before initial qualifying event will require significantly more time and dedication.
Does he have any more specific questions?
Allison