Dr. Paavo Airola's book listed in the books list on this forum, is my favorite. It has excellent testimonials and step by step instructions. "Juicing for Life" by Cheriie Calbom and Maureen Keane gives all kinds of juice recipes for all kinds of ailments, including obesity/overweight(as it's listed in the book).
In my experience, the amount of juice I drank didn't affect my weight loss at all. You lose the most at the beginning, then you start to slow down. Eventually, you get to a point that you don't lose weight anymore. It's up to your body.
You CAN drink the same juices everyday. I can't even imagine HOW an allergy would develope from it...
Make sure you're getting in a good amount of juice and water. A good resource book will really help you figure what a good amount is. You don't want to damage your body in the persuit of weight loss. hth :)