Sorry but i don't have any experience with propecia.. if you feel like the treatment is necessary, then i'm sure that there are other guys on the forum that can give you a fair advice!
Here's my opinion: From the pictures I don't see any signs of balding, just relax and see how your vitamin regimen works. It could be stress related. Start treatment when you are sure it's male pattern baldness :)
you hair density seems normal, since you are still 19; you hairline might be maturing and stay like this for your entire life, but there's also the probability of further but slow thinning over the next years. You should pay attention to it and treat it if you see further thinning ;)
when your hair density gets smaller due to a shed or thinning, you are more likely to feel the wind on your scalp. The reason of your cold sensation might be simply related to your thinning.
It could be due to minoxidil, even topical use may have effect elsewhere on your body since the half time of the molecule is around 22 hours... remember: the skin is also absorbing molecules from the outside world to cope with dehydration. minoxidil can be present in your blood stream in small...