I fasted to help myself get clean. Fasting does not stress the body. Digestion is the most complex function of the body so fasting does take stress off the body.
But....you may develop some unpleasant "detoxification" symptoms as fasting will help the body to push out toxins so don't be surprized if you start having "flu like"symptoms. I think it would be a good idea to consult with a Dr. who practices natural medicine such as a Naturepath or a Chiropractor who knows how to monitor your symptoms and can give you good advice on how to conduct your fast.
I don't think heavy exercise is good to do while fasting. Being that you are detoxing from alcohol I think it would most likely be a good idea to not use to use fruit juices and stick with vegetable juices because of the high sugar content in fruit. It is a known fact that almost all alcoholics have a sugar imbalance which contributes greatly to cravings..