Rogaine does not cause shedding in every case, but shedding is seen as a good sign. The problem I had with the foam was that the amount shedded was unacceptable. There was an area with hair which went completely bald, but as stated has returned since.
I have only ever used 5% rogaine and as far I am aware, minoxidil has no effect on "sexual" issues.
Proscar does come with the possibilty of "sexual" side effects, however, they are rare and in most cases short-lived (even with continued use).
There are very few (if any) medications in the world that come with no chances of side effects, hairloss meds included.
Both Proscar and Rogaine are usually very well tolerated and any side effects diminish if you stop taking them.
Sadly, the only way to see how you will react is to try.