Good luck Technics:
As you can see from my signature, i had my surgery last year and revision just last week. Your question is very good. I think you should prepare your self better before you go for surgery to get the optimum result. Not like me, just go for surgery first and then do rest. It all depends on your body (like you slim or fat). If you are fatty person, I think your chest size may be bigger than the person who is slim. Like me, I was almost 205 lbs and size 39 before surgery. And my boobs WERE bigger than a apple. Yes !!! But those were all fat and gland tissues. After surgery, Fielding removed most of the gland tissue and kept some fat in there to have my skin and nipple set properly. Else, nipple may indent and that looks worst when you are without shirts. So he has to keep some fat there after surgery. And that's the reason, I went for revision to remove that fat again after a year, and after all skin settled a bit.
Now, as per your question, I think it will be better to reduce some weight before surgery. Specially some fat near boobs. Here, Please Keep in mind that whatever you do, how heavy you go with weights, your gland tissue won't go away. It will be just fat that might diapear. Gland never go away with weights training or diet. And also note that after you lose good size weight, you may look little worst than before as your boobs may stuck out more than before. But by the time, you will be ready for the surgery. So it's won't bother you that much. I think, If I have to go thrught this again from zero, I would definetly reduce some good weight from my body and specially near chest area. And than go for surgery. Reason, once you lose most of the fat by gyme or diet, you have skip the one important step after surgery, to shrink the skin and fear of indent of nipple. Think about it that if you have small size to begin with, you will have less to worry. So again, it's all depends on your size of boobs. I had really big size to begin with. So I went twice and still I won;t be expecting the flat out chest. So I think try to reduce whatever you can and then go for surgery just to reomve gland. Again said, gland won't go whatever you do. You have to go for surgery to remove.
And importantly about scarring. Don't worry my friend. I can tell you that mine were all gone just in 4-6 months. No one can tell that what I went through near my nipple. He did great job.
Good Luck and hope this will help. Come back if you have any more questions.