There are a few things to consider.
There's the skeleton, which won't appreciably change with post-pubertal HRT. While the skeletal systems of young children are more or less identical across sex, there are noticeable differences once the two sexes have gone through puberty. By far, the greatest level of sexual dimorphism in the human skeleton is observed in the pelvis. This is the trait most often used to determine the sex of skeletons. This is a really rough way of putting it, since it's not quite this simple, but yes, the pelvis of a person who matured as female will be wider than a person who matured as a male. That contributes slightly to the "wider hips" of women.
But the difference in width is not really enormous. The biggest differences in the male and female pelvis are other things. And with most other parts of the skeleton, there are large numbers of people who stray into the proportion ranges of the other gender (in other words, the ranges have significant overlap). So skeletal proportions are not something which, by themselves, observers flag as out of the ordinary.
The major difference in body definition is down to two things: body fat and muscle mass. Muscle mass definitely has a huge hormonal component. Men are far more prone to accumulating muscle mass in the upper body. This is why even dedicated female body builders never develop quite the mass you see in their male bodybuilder counterparts. So yes, when you are on HRT and antiandrogens, you will begin to significantly lose this upper body muscle mass after a few months. You will have less chest, shoulder, and arm muscle definition, and you will generally appear "smaller" above the waist.
Body fat distribution also has a very large hormonal component. Women naturally accumulate large amounts of fat on the hips, while having almost none around the waist (the smallest diameter part of the torso, generally). Likewise, while glandular tissue makes up some of the volume of female breasts, most of it is also fat. Fat distribution is what primarily creates a woman's "hourglass" shape and fills out her feminine features. This will naturally change on hormones.
Bottom line, you should see a marked improvement. Most of the things that need to change, will change. And the things that don't? They shouldn't be a big-enough issue to raise red flags by themselves.
If this is a big concern of yours, I would recommend you begin the process in a fair degree of physical fitness, as having correct body fat distribution is a big component of appearing female below the neck (well, depending on how you choose to dress). Women, and this is primarily a hormonal difference, have a much more difficult time shedding body fat than men. This is especially true of areas not typically used for fat storage in women. So it would be easier to lose it now than after-the-fact.
