Not the OP, but knowing someone who’s been through something similar I can answer a few of your questions. She had this surgery nearly two decades ago, so modern procedures may be completely different:

• Adipose tissue and skin from the belly was moved to the breast. The tissue was left completely intact, including nerves and blood vessels.
• A nipple was tattooed onto her skin, no tissue sculpting, etc.
• Since all the nerves and vascular system was intact, any sensation on her new ‘breast’ was still mapped to her belly.
• Her new breast was sculpted to be the same size and shape as the healthy one.
• Since her new breast was made with belly tissue, any weight gain/loss may be uneven compared to her other breast.