New to fasting!

This will be my fist water fast. I plan on doing a bunch of cleanses like colon, liver, kidney etc then do the fast. I want to clean my body of toxins and lose weight. I read on the sight to start out on a 3 day fast then work my way up to more days. How often should I do a water fast? Also, I get very light headed if I don't eat, would it be so terrible to have a glass of juice every once in awhile during a fast. I don't want to pass out doing this...I guess I would like some advice since I don't know anyone that has done this. My friends and family think I'm nuts for trying this. You can email me at my personal email if you'd like l_drollinger@hotmail.com
Thank you Lisa