It sounds like you've done a lot of your homework. To address your questions:
Scarring - The character of your shoulder scars is actually typical of shoulder scars, as well as the nature of the original injury (a burn). This is not clearly predictive of the scars that might form from a surgical intervention such as gynecomastia surgery. For one, the location of scars for this surgery allows for the scars to be better hidden than a burn on the shoulder. Also, in the majority of patients who do not have a genetic predisposition toward bad scars, these scars fade very well and are barely perceptible over time.
Anesthesia - I used to do all of my procedures with conscious sedation or "twilight sleep," and if your surgeon is comfortable with this approach, I found it to be adequate. I'm less enthusiastic about straight local anesthesia, since it may limit your surgeon if you're not able to tolerate the surgery, and he or she doesn't have the ability to use medications to make you more comfortable. If you suddenly find that you're jumping off of the table due to discomfort, your surgeon only has the option of trying to use more local, or you would need some way to get pain medication and sedation on board quickly, and that is not usually achievable without an intravenous option. If you're young and healthy, general anesthesia has very low risk. As any anesthesiologist will tell you, your drive to and from the hospital is far more risky than your anesthetic!
Compression vests - I use compression for 4 weeks. Some surgeons go for longer. Some don't use compression. I think that all of the surgeons on this forum use compression. As for vests versus ace wraps, I find that the ace wraps don't stay in place, nor do they give even compression. Over the weeks after surgery, it's difficult to put them on alone, whereas a vest can be taken on and off independently and usually provide even compression.
Choosing a surgeon - It sounds like you've found someone who does a lot of gynecomastia surgery, so as long as you're comfortable with him as well, and you've seen good results in his patients, you should be all set.
Good luck.
Rick Silverman