I think with Master-Cleanse ten days is ideal. If you were water fasting, three days would be the max at first, then gradually fasting longer as the body cleanses. Joel Fuhrman, who is an expert in water only fasting, suggests losing almost all the excess weight before beginning an extended fast. Paul Bragg, in his book "The Miracle Of Fasting" describes a fast he prescribed for an actress that combines periods of healthy eating with gradually longer fasts added. Master Cleanse is so much more gentle than water only, and its easier to do it for longer periods; however, I still believe a series of shorter fasts is best for weight loss. Another bonus is that you are training yourself to eat right between fasting so you're not suddenly back on food and unprepared to begin a whole new lifestyle of eating and eating management.
I'm an emotional eater and could really relate to a lot of what you wrote.