1. Light is not needed. Keep the temp at whatever temp your betta will be in
2. Gravel vac should be ok to use
3. Not sure
4. You may get away with it - not sure though
5. It should, BUT, you will be dividing your tank 5-6 ways? Sounds like a bit much for a 10 gallon. Keep in mind that a 10 gal is only 24 inches ling (standard size). 3-4 should be better.
EDIT: OH, I think you are talking about a sorority
lol. I think it will be fine. have you tried checking http://aqadvisor.com/