I've done one round of fat transfer as part of my quite extensive lipo sculpting/contouring surgery. Second round coming soon, I'll answer the questions for you.
1. Typical transfer volume in total is between 200cc - 600cc. Mine was around 650cc in total as my wide breasts allow a lot to be done due to surface area. Bigger surface area and lower density allows bigger transfer volumes in one go. My breasts are very dense, but they're so wide I can take more than usual in one go. Typically surgeons tend to overfill for about 50cc to compensate for losing some.
2. Typically you retain about 50-75% of the volume, but you can retain as much as over 90%, this is a bit of luck and genetics at play because everyone has their own limits on how many fat cells their breast tissue can "latch" onto. I retained almost all of the volume when swelling went down and what ever I lost, natural growth soon made up for. The biggest difference was in shape and the change was rather dramatic. I gained less than a cup size in volume because I'm at the point where cup size differences are quite large. Check out my thread for the latest timeline, that shows perfectly what the transfer did.
3. Its very typical to go for more than one round of transfer, I'm booked for one more and I might opt for one or two on top of that. Its slower to do than implants which give full volume in one go, but result is 100% natural. It doesn't change breast shape much, but can enhance natural shape in multitude of ways and its very accurate.
4. Typical price for one round is about 2000-3000$ or so unless you pick shady super cheap option. Clinics often sell a sort of bulk of these, so there's series of them done and all is lumped in one payment. That might be bit cheaper than booking one at a time. Many places sell this as part of body contouring which might make it more affordable if a bigger proportion change is planned.
5. Fat cells after transfer retain their "cell location" and behaviour, this means that weight gain or loss will make boobs grow or deflate. Transfer area doesn't matter as much as some say, but often closer to the goal spot is better. Mine was a mixed one last time and second round will be lower belly fat which is awesome as that's where I always gain the most and fastest. This means that future weight gain will make my breasts grow a lot bigger.
6. Complication risk is typically very low, but complications of fat transfers can be very dangerous. So choose a reputable clinic and top class surgeon, pay a bit of a premium if possible. This isn't to be toyed with even though its one of the safer surgeries there is. Recovery is quite easy but first week can be extremely painful. If they use the modern waterjet system for lipo, that's far more gentle and it makes easier recovery too. I got this option as the Finnish clinic is very up to date with techniques.
7. I would choose fat transfer for detailed shaping, natural result, somewhat affordable cost and low complication risk. For raw volume and radical shape changes, I would rather pick implants. But then again if shape doesn't need to be changed but enhances and several transfers can be done, volume can easily exceed typical implants too so that's one more pro for fat transfers.
I'm supposed to get my second operation booked soon, I should get it done in about a month or bit more, after that I'll be here ready for an AMA.