Perhaps I'm overthinking this, but, the literature that I have read says that most breast growth happens between 3 months and 2 years after the start of HRT. My concern is that I had initially figured that I would go on a low-dose regime (yes, I know, dosages not allowed!) for about two years until I retire, then ramp up to full transition doses. Will this affect the amount of growth that I have during that 3month-2year window, or will I probably be able to make up for that once I go to a full dose in a couple of years? Anyone have any experience with this specific concern?

I plan on asking my endo this exact question when I go for my first follow-up this week, but I wanted to go armed with anecdotal info. 

You are overthinking it. I was on a somewhat limited treatment for years without much growth. Then I was off HRT for about 10 years and I returned to it a little over a year ago. What I am now on even at a half dose is far more effective and I am seeing breast growth that I never expected. The growth will take place whenever sufficient estrogen is available up to your genetic potential. Low dose will not harm your future potential.

Growth and changes will occur for a lifetime and breast growth in pubertal girls takes more than 2 yrs, more like 3-4 yrs and sometimes longer to mature.