Good evening Dani,
Any kind of surgery is going to be permanent. I am sure you know that. I am not gender fluid, so I sometimes have a bit of difficulty understanding your feelings other than the effects of gender dysphoria in general as it applies to my own situation.
For me, surgery was the end goal for the treatment for my gender dysphoria. I never wanted to go back to what I was years ago.
Since you are focused on
"top surgery", are you considering full mastectomy or maybe breast reduction? Is either of these acceptable on those days you do not feel intensely male?
You mentioned building up your pectoralis muscles. I tried that in my younger days when I tried to work my dysphoria out of me. Needless to say, this did not work for me, but I know how to do it. First you need Testosterone and a lot of it. Your blood levels need to be in the
strapping young man range, also known as
almost off the scale.

Next you have to work out for years, either on the job, if manual labor or in the gym. Yes, you can find a surgeon who will put hard silicone implants in your chest, but this is not the same as a pair of powerful pecks.
Whatever you decide to do is going to be your decision. I can only tell you what worked for me. The only advice I have is you must have realistic expectations. Surgery is permanent.