Something that should also be kept in mind is proper diet and exercise. If you eat healthy and get your heart rate up (treadmills etc. are great) you can keep decent muscle tone, lower unwanted body fat, but still not hinder ample enough fat content to get a more feminine shape. The only problem is, natal males don't have hips as wide as a females, so development in that area isn't usually going to be the same as a natal female. Basically you shouldn't end up a "fat chick" unless you overeat and don't move around, just like anyone else, trans or not.
Of course, I'm not speaking from absolute fact, everyone reacts to hormones, diet and exercise differently! Besides, even if you only end up with A or B breasts, is that really a bad thing? Pushup padded bras can go a long way without having to resort to possibly risky and unnecessary surgery. Breast development, even in natal girls, often takes several years to complete so don't get discouraged and get implants within the first year as your natural breasts will not be done growing in yet! I have heard that trans women often get impatient and then get implants way too soon only to have a sudden growth spurt, then they end up getting the implants removed or replaced with smaller ones.
I personally would just let the hormones work their magic for at least a year. Eat well, exercise, and see what happens. =]
No matter what, being healthy should be priority number one!
~April