Hi Daniel, I was a regular user of Pro Banthine several years ago for about 18 months.
1. Other side effects for me were blurry vision, a strange tight feeling behind the eyes and just feeling a bit "off". Hard to explain but it was like I didn't quite feel myself while on it. The dry mouth/throat was the worst side effect as it meant literally every bite of food had to be washed down. On the upside I could finally eat spicy food in public.
2. No not that I recall
3. About 6 hours if memory serves
4. Sorry I don't know, got mine through NHS
If you have a general sweating issue all over the body I would recommend this as a possible solution. If you have a more localised issue (like hands) I would suggest trying other treatments.
Hope that helped