Should I increase my calories or carbs to support the fat transfer in the first few weeks?

If you are in good general health, and all medical conditions have been managed; adequate protein intake as well as a multivitamin can be useful. No need to increase calories or carbs.
Kenneth Hughes, MD, ABPS Board Certified Plastic Surgeon
Los Angeles, CA

Dear likelyoffspring,
I understand your concern. It is best that you consult your plastic surgeon regarding post operative care and management (i.e including massage techniques and timing) specific to your case. Your surgeon knows your condition well and has preferences on when and what to use for faster healing and recovery. Post operative care and management depends on the type of surgery performed and the technique used during surgery among other factors.It is best, however, that you follow your plastic surgeon's advice on post operative care management for a smooth and faster healing and recovery.
Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

You do need adequate protein to heal, and I recommend adequate fats, plus vitamins and minerals to heal well.

Your short term diet won't affect the long term result after fat grafting.  Just do your normal routine.

Since you have a low normal BMI, I am surprised that your surgeon was able to transfer 400 cc of fat. If you gain weight, the transferred fat will increase in size.  I don't think that increasing your carbs or calories will have any effect on whether or not the transferred fat will survive. I think that fat transfer to the breast is a poor choice for breast augmentation. If you had 200 cc of fat injected into each breast, you would be lucky if 100 cc of the fat survives. An increase in 100 cc in size of most women's  breasts will not result in much of a chance in the appearance of her breasts. If your breasts were very small to begin with, a 100 cc increase in size could result in a noticeable change in the size of your breasts.