Donna is absolutely right: most people see and hear what they exoect to see and hear. Of course people will notice that you are changing, but they will just think that you are losing weight, that you are sick, blah, blah, blah
Nonetheless, third parties will start calling you ma'am soon. It started to happen to me about two months ago, i.e. almost six months into HRT: I would go to work in guy mode and then go sopping or go to the grocery store, and people would call me ma'am and/or hold doors open for me, and stuff. I have changed jobs and went to the new job as myself: the new company knows me as Andrea, a female employee.
My thing is that I have always been very feminine, since childhood, so people, long before I started HRT, always thought I was a very feminine gay guy. My voice is also feminine, people have always thougtht I was a woman when they heard my voice on the phone, and even when asked my name and replied with a very guy name, they would still call me ma'am.
Anyway, good luck, and don't worry too much about breasts: there are men, manly, straight men, who have breasts, and girlie girls who are flat or near flat. My little sister in law is one those women with basically no breasts whatsoever, but nobody would ever doubt, even for a split second, that she is not a girl.
Love,
Andrea
PS Before the "lucky you" 's start, I am not that lucky: I have feminine facial features, like a soft, small jaw, and stuff, but I have indeed lost hair!!!!! Not a very feminine trait. Wigs are the only way at the moment, although HRT is making my hair quickly fill in like crazy.