DCHR,
Lots of info for you. Good job by getting on this forum and asking questions!
As long as you are going to commit to a Hair Transplant, and you show the typical balding pattern, I feel it is worth the risk of any side effects to use finasteride.
I believe the generic finasteride is just as good as Propecia, and you can order it here for the best prices I could find:
http://www.canadadrugs.com
If you can wait until you are 30 or so, your chances of having long term success with a Hair Transplant will only increase, as the pattern will be more evident and a good doctor will be able to effectively estimate where the hairline should go.
Best of Luck!
Panama Jimmy