Thank you for the question.
It is possible to reduce the breasts size very significantly. Sometimes when patients want “almost nothing left” the reduction should be done in 2 stages. The concern with the amount of tissue removed is related to blood flow to the remaining tissue; if too much tissue is removed in one operation the blood flow to the remaining tissue (including nipple/areola) may be compromised. Part of the tissue that is left in place is called the “pedicle"; this segment of tissue is responsible for delivering the blood supply to the nipple/areola tissue. If the pedicle is made too small (in the effort to reduce the breasts as much as possible) then patient will likely have problems with tissue survival. Doing the procedure in more than one stage allows the tissues to acclimate to the surgically decreased blood flow before further tissue removal (and potentially further decreased blood flow) occurs ( with the 2nd stage operation).
The other concern with overly aggressive breast reduction surgery is patient dissatisfaction afterwards. It is not unusual for patients who have lived with very large breasts to want to have as much as possible removed. Care must be taken to be judicious in this removal to avoid an outcome where the breasts are too small in relation (proportionately) to the patient's other body parts. Again, it is not uncommon, for patients' breasts to become smaller ( after the breast reduction procedure) with time and/or weight loss- breast augmentation may become necessary to achieve the patient size goals.
It will behoove you to seek consultation in person with a well experienced board-certified plastic surgeon.
I hope this helps.