#1: No. No, not to any appreciable extent. (IMPO)
#2: Cycle or not, if one uses Propecia, or dutasteride, or minoxidil for that matter, one will "catch up" to one's natural state of baldness once the drug is discontinued. If you start Proscar, keep it up until something better is released. Or don't start it at all. It's not rational to just take it during a cycle.
I know of no evidence that finasteride is effective or ineffective when used for short periods of high test levels, such as a cycle. The studies were all done on men with normal range testosterone levels.
I am prone to androgenetic alopecia (MPB), therefore, I use Propecia all the time, cycle or no cycle.
You may refer to my post on hair loss on the articles section of this board.