I take it that 19 is the age you come of age in your country/state? In most countries you have to wait until you become legally independent before you transition legally (that is: can change the gender designation in your passport).
Many allow for a social transformation before that time, though. In the sense that you can come out and live as your target gender. This also applies to those who are not of age, if their parents/legal guardians agree. So that should be possible, even before you turn 19.
In some areas doctors may also provide you with puberty blockers, that will postpone some of the more masculining effects of testosterone, making it easier to pass after you start hormone replacement therapy. If you decide that you do not want to transition, puberty will restart when you drop the blockers. I do realize that at 6.4 feet this might be too late for you, but it is worth considering all the same. There are other sex characteristics that have not fully developed at 17, and that might make a diffference in the future.
You do not say whether you have been talking to a gender therapist or a doctor about this. If you haven't, I suggest that you do. He or she might help you ask the right questions, and you will have to get in touch with the health system anyway, if you end up transitioning.
(Note that there are some bad seeds among therapists as well. Tell us about it if he or she makes you feel uncomfortable. We can help you sort it out.)
I am not a crossdresser myself. I think that I would have been better of if I was, but that's the way it is, so I hope some of our other members may give you some advice regarding crossdressing.
There are online stores that cater to male to female crossdressers, and which also cover larger sizes. In some areas you might find crossdresser clubs where crossdressers meet and discuss clothing and make-up. In a few cities you will also find crossdresser salons where the staff helps you transform. Their services are not free, though.
If you have female friends who would like to help you crossdress, that is an opportunity you might make use of. Maybe they can help you shop for clothes?
I am so glad your friends and your parents support you. That makes a huge difference.