It depends. If the doctor puts you on antibiotics and pain medication after surgery you don’t want to be fasting while on those.
I’d recommend waiting a week or so after the surgery to start fasting.
It definitely helps with healing. I did it after childbirth (after breastfeeding stopped, of course) and it made the post partum healing faster.
Not my place to say but you dont need to get boob implants. Most guys prefer natural boobs, even if they are on the smaller side. Im sure you’ve heard it before but just wanted to throw that out there.