have you ever done a juice fast before? if not, i would suggest building up to one, or even start with 3 day ones- 7 days will be tough and you should be very mentally prepared. the first 3 days are the hardest. research a lot and you will find answers to most of your questions. consume as much juice as you want, or at least for the first 3 days to make it easier on you. drink juices that are made from organic fruits and vegetables from a juicer. if you don't have a juicer, do not go on a juice fast until you do, as it can be unhealthy. store bought juices are pasteurized and unhealthy for the purposes you fast for. hope that helps. good luck on your journey- i love juice fasting. tomorrow i am going on a 3 day water fast.
ps. nobody really posts here. try fasting for weight loss or water fasting- they're really helpful, but water fasting..is for water and not juice lol! :)