Percy may be suffering from a condition called Psychogenic Alopecia, this can be obcessive/compusive or autoimmune in nature. You can read about it here:
There is also a stress of allergy based skin issue called Miliary dermatitis:
This responds to steroids but will recur if the allergin is not removed.He may have had a flea issue in hiis prior location.
The OCD type of Alopecia should respond to valium or clomacalm. The autoimmune is usually treated with steroids. However, prolonged use of steroids can cause kidney disfuntion.
This can be a result of stress or allergy due to corn and gluten in his food. I would suggest you try some homeopathic remedies from the following sites:
Many people use rescue remedy (pet supply)as that is a flower essence and can be very helpful. I also suggest you get some onesies made for human infants to keep the area inaccessable. . These have snaps or zippers so he will not be able to reach the spots.Since the area is mostly on the legs he may be allergic to scented cat litter.
Try completely natural food, at http://www.petfooddirect.com/ if he is eating anything with corn or gluten.
He may just need time to settle in and calm down. You can get a feliway plug in www.catfaeries.com
I know this is a lot to cope with for a rescue kitty. May God bless you for saving him.
Please let me know how he is doing. If you have any more questions, please do not hesitate to ask. I will be more than happy to try and help in any way possible.