Darryl,
1) The suggested activity factor for CrossFit only is 0.7.
2) The chart is actually pretty accurate, provided you measured properly. I have very thin wrists as well, and the chart estimated me at 10%. My Tanita scale claims around 11%.
The rib showing/love handles/6-pack showing numbers are only rough estimates.
3) Everybody does it differently. Find out what works best for you. If you don't eat a snack before and you bonk, you should eat. If you eat a snack before and you barf, you probably shouldn't eat, at least not so close to the workout.
My general advice: Relax, figure out what's best for you and your body, and gradually adjust as you learn.
