I had Diep Flap surgery after a double mastectomy back in 2016 and am so glad I put myself through it and still very pleased with the results. It is a long operation (mine longer as both were getting done) and you will have to spend at least 5 days in hospital depending on your recovery and fitness. The first 24 hours post surgery quite bad but quickly gets easier. Best advise, get yourself fit for surgery, eat healthy, stop drinking (and definitely stop smoking), and give your body everything it needs to recover quickly. Your surgeon guides you through all the decisions and based on amount of flap available from your abdomen, will be the basis on how large, or small you want your new breasts to be. If you are only having one done, they will match the size to your existing breast. Have to be realistic about what can be achieved. Only after your new breasts have settled down, healed etc, can you get nipple reconstruction (I had that done as well and is the icing on the cake so to speak). Tattoo artists can also do wonders if you have had enough surgery by then.
You will have scars, quite a lot but they minimise with time but will always be there. Recovery takes time and if you are into fitness like me, will have to ease up a lot to let your body heal.
Hope this helps. Any more questions, I will be happy to answer.