Yeah bro you're right in that zone where if you stop it with finasteride you're good to go, but if you let it keep receding you'll regret it and will go from a guy with a high but passable hairline to a baldcel. I was where you are now and decided not to take it, progressed to a Norwood 3 and now I gotta get a transplant to get a hairline back. You could get one where you are but I think some docs would advise you to mull over just how much your current hairline bothers you. Being 31 and stable on finasteride for 4 years is a good place to be for a little hair transplant though if you wanted to close the temples a little bit. Who knows, the finasteride might give you some good regrowth as well.
So i'm doing an email consultation with a doctor from Dr. Konior's office, and she states that she starts patients on 1 mg of propecia for day.