My personal opinion is that if you have that many questions about fasting, you shouldn't be thinking about a 40 day fast. You should be reading up on water fasting. Dr Shelton would be a good start.
Answers to your questions are, No, No, and depends on the length of the fast as to how you break a fast.
As for the psoriasis, Colloidal Silver will take care of it. Keep the area as wet with CS as much as you can. Spray, or use some kind of cloth that you can keep wet.