If you are going on testosterone, you must be prepared for the possibility of male pattern baldness. I have been on T for 6 months, and I am already experiencing hair loss (my hair is longer, so it's quite obvious when each day my sweatshirt hood looks like a Persian cat's been sitting in it). My dad has a full head of hair at 60. Only one of my male relatives on my mom's side is bald (dad's side is all dead, but since he's not bald, his genetics aren't the problem). It CAN HAPPEN TO YOU. For reasons still unknown, hair loss is just as or perhaps MORE common in HRT-treated FTMs than in cismales (I've read studies ranging from 10% to 40% experiencing significant hair loss within the first 5 to 10 years of being on T). Since the X chromosome is much bigger than the Y chromosome, it is tremendously likely that the major genes which determine who loses his hair are on the X chromosome, and that since we have 2 X chromosomes, we experience a "double jeopardy" sort of situation. This would only be true if the genetic alleles which trigger hair loss (their identitites are still in debate) are dominant (having 1 = you have the trait). From what I've seen of the FTM population, it seems very likely that the allele(s) IS (are) dominant, and that's why there are so many bald FTMs. There could of course be other explanations, but baldness is for one reason or another quite common in FTMs who have been on T for a long time.
On the bright side, FTMs go bald by the same biological mechanisms that cismales go bald – DHT chokes off the nutrient supply to susceptible hair follicles so that the hairs die off one by one. This means that finasteride (Propecia), which blocks the conversion of free testosterone to DHT, works just as well for FTMS as for cismales. Of course, if an FTM takes finasteride, the effects of HRT that he might WANT may also be reduced (the most prominent one being growth of facial hair. DHT stimulates facial hair growth while discouraging the survival of head hair follicles. I have no idea why.).
