Hi Kelly. Congratulation on nearing the end of your PhD.
1). You're about my size. From my experience, you shouldn't have any issues with breast development for a bit. You will most likely have a year or two before you really have an issue with hiding things. Provided you don't run around in skin tight shirts all the time. A quality button up dress shirt over a t-shirt would make almost all breast growth undetectable for at least a year. With that being said, I'd suspect that after 9 months or so you'd be able to finesse some notable breasts with the right pushup bra if you were so inclined.
2). I can't really say "how long", or "if" you should try to hide it. That's a very personal decision. I'll just say that you'll have a year or two of "grace" to make that decision for yourself. I'd say 9 to 24 months is your twilight time. You are most likely going to have subtle changes in skin, hair, complexion, and breast growth during that window. I wouldn't say anything staggering... but it is a time where you can go about your male life with some nice skin and little thicker hair, or with a splash of makeup and the right clothes that you'll look quite feminine.
3). From my experience, there's only two things that could really "mess" with your concentration. 1). One would be if you get a ridiculously high dose of Estrogen, or that you're susceptible to mood swings at a normal dose. However, you should be able to dial that in within a week or two. For example, I started on IM injections and I noticed the difference in mood and temperament for the first couple weeks as I ran the course of the cycle. After that I got used to it and adjusted. 2).The only other thing that could mess with your concentration is yourself. After all, when transition is something that you really really want you're going to be really excited and it can stay on your mind. Checking for changes, worrying about getting clocked, wanting to share all your excitement with friends, and dreaming of fancy dresses... it can all be very distracting if you let it.
4). I can't say if or when you should tell your friends about it... again, very personal. However, I would suggest picking one trusted friend (that you've come out to) about being on Hormones. Just so you'll have someone to share with. Something so exciting, is very difficult to keep to yourself... having a sounding board to bounce ideas and feelings off of can be a huge help. I'd say from my experience around the boards over the past 5 or 6 years, you're more at risk of outing yourself to those around you out of joy or frustration with the secret than you are from being given away by your body. Just a thought.
Keep in mind that the changes will be subtle, but cumulative.
Hope it helps,
Victoria