When I was instructing at Riddle I typically had 6-8 students, though often in the fall when we were swamped I'd stretch my limits and that would go up to 12-14 at times. Usually worked 6 days/week. Obviously some people were not flown as often as they'd like in that case, but we were short on CFIs at the time. 8 is a good number though if you want to fly your students often enough, but not exhaust yourself. Maybe find a few more if some of those are part-timers that fly on the weekends, etc. One good thing about working your butt off though when you CFI...if you move on to the airlines, the schedule seems easy!