Would two breast fat transfers mean twice the amount of scars? Can lasers address the scarring?

The best way to minimize scars is to make the fewest number of incisions possible without compromising the quality of work done. The scars from liposuction will continue to fade in most cases for at least one year.  In general, 200 cc per breast is typically the upper limit of fat injection recommended by most plastic surgeons.  It is not that more cannot be injected; but on average, this has been determined to be the most that can be expected to live during one transfer.  The fat must be injected through multiple planes in small amounts to the tissue through one tiny incision under each breast.  
Fat transfer to the breast could improve the fullness of the breast, particularly at the top of the breast. If you want more than a one cup size increase, implants are probably a better choice.  If you want fat grafting, this may require multiple treatments to reach the size you desire.   About 50% of the fat obtains permanence.  
Kenneth Hughes, MD, Board Certified Plastic Surgeon
Los Angeles, CA

Usually for the second fat transfer, the same incisions can be used if fat is removed from the same area as with the first transfer. Micro-needling or laser could help improve scarring in most people.

I make every attempt to do this procedure in a single stage.  Liposuction incision should be extremely small:  maybe 2.0mm.  These can be hidden in your panty line.  I treat all incisions with scar recovery gel.  If a scar persists after 6 months I use microneedling to help with the appearance.