Hey Darkwolf,
As stated before, everyone's experience is different so I can only tell you mine and I can't guarantee you would experience the same.
The quickest changes for me were lower growth and voice. The lower growth happened surprisingly quickly (noticed growth within a week, largest change was within the first two months so far) but the only way I needed to really "get used to it" was in regards to jerking off with different anatomy than before, and it did get quite sensitive at a time during which I couldn't pack and had to wear really soft underwear. My voice itself hasn't changed as much as I'd hoped but I felt it changing very early on. My throat for very sore and I felt like I was getting sick within the first week and it stayed for a while before going away. It comes back whenever my voice is about to drop significantly again.
I was actually concerned about changes coming too quickly, which is part of why I am on a low dose, however, I've actually wished changes would come quicker. When I look subjectively at my changes, I know that I'm about on par with other guys on 5 months, yet I do feel like I'm falling behind in places like leg hair and the amount my voice has dropped.
I have not experienced many body shape changes and I've felt dysphoric more than before recently, however, I believe it is because I went from passing 75% of the time to now about 10% of the time, and nobody really knows why. My face is actually more masculine than it used to be. So I have experienced more body dysphoria because of that.
It's definitely fine to be on hormones before surgery, some people think even better. You may get nicer results if you've got pecs to place your nipples with. Most guys start hormones first, it's very common.
My personal experience with 'regrettable' changes is that things change slowly enough that you've got plenty of time to stop T before a change progresses further, with the only exception of lower growth. There are permanent changes on T like body hair and voice deepening, but these happen slowly over time, so if it begins to make you uncomfortable, you can stop before it gets worse. Of course, you should still be sure that you want to start, but I know that many people still have doubt in the back of their mind, and that can relieve it. I knew I needed to start T if I wanted to have a life, but I still sometimes had doubts. As soon as I started T however, I knew this was right. I got so excited for the changes and I wish things would happen quicker- I definitely am not as afraid anymore. The doubts are gone.