Bra size:
I'm sorry, but I think that I can't say much for your bra size; that is an incredibly individual issue to overcome. I've seen it shared often enough that most women wear an incorrect bra size. I think maybe it would help you to consider some Googling on the various bra types available to fit breasts that are far apart. When you feel comfortable, there are also many clothing store workers who have a lot of experience in measuring bra size and can help you to select the right fit. It really helps to get multiple opinions, too.
Breast formation:
Breast formation is very individual as well. It could come in quickly or very slowly. Their shape could change dramatically over time. Many girls continue to see development into their early 20s despite growth beginning at age 8 - 13.
I think it's also worth mentioning: my boyfriend recently pointed out to me that it isn't uncommon for trans women/girls to have frustrations about being underdeveloped. Especially in regard to shape, a cone type form is not infrequent. I think he pulled that statement from the fact that some implant surgeons say this is a common concern they hear from women like us. Please don't be discouraged if you continue to be disappointed by your shape, it isn't all too uncommon for cis women to feel this frustration as well. Breast augmentation is also reasonably affordable with some smart saving, if you feel okay with that sort of thing.
Anecdotal experience:
I have been on HRT for a little over four years and I still occasionally find myself with growth soreness (as I type this, even). I was an A cup until about a year ago, and even that size took ages to come in, when my boobs suddenly sprang up again and shuttled my bra size healthily into the B range. I have also lost approximately 50 pounds (currently 160 at 5'9") since mid-2013 and, contrary to what I often read online, it actually helped my chest stand out more. I also used to have to deal with more of a cone shape, but that has rounded off considerably over the past year (especially when the area is aroused).
I was really surprised by my current bout of soreness, but am also happy that development continues several years down the line. I had just about given up even though I knew continued growth was possible.
Other stuff, silliness:
You can't be certain of your outcome until years and years down the road. It can be really frustrating, but please keep your chin up! You might just find yourself with pleasant results.
I have to express, too, that the word "breasts" is so weird to me. I find it so difficult to say or type and not feel awkward. Maybe it's a habit/outlook I picked up from friends, but really, I feel like "breast" is either something in the grocery or an alien appendage.
