Will large implants (1000 CC) affect breastfeeding in the future?

Family planning is a somewhat fluid process which may or may not conform to a schedule. Thus it becomes difficult to plan elective surgery around events that may come at some point in the future.
The question of timing of elective body contouring as it relates to pregnancy is ultimately dependent upon expectations. There are a number of changes that occur during pregnancy (some more reversible than others) which may potentially compromise your overall aesthetic result. With this in mind, the best thing that can be done is understanding how your body may (or may not) change post pregnancy and preparing appropriately.
It is important to remember that pregnancy changes more than just your weight. There will be changes in muscle and skin tone which in some cases will not return to baseline. The safest recommendation is to maintain a healthy lifestyle (diet and exercise) through pregnancy and afterwards. This will ensure a greater likelihood of a return to form. This is by no means a guarantee but it will help. Lastly, be prepared for the possibility (eventuality) of further procedures in the future to regain your pre-pregnancy form.
Additionally, the presence of implants and a prior lift should not influence your decision to breast feed. You should be able to safely breast feed regardless of prior surgery and should consider doing so for the sake of the newborn. There is mountains of data regarding the immunologic benefits of breastfeeding.
In summary, with regards to your specific question, implant size will not impact breastfeeding. Ductal integrity regardless of size is operative technique dependent.
As always, discuss your concerns with a board certified plastic surgeon.

Not all women are naturally able to breast feed but in my experience if they were able they still were able. My patients have the implants placed part behind or under the muscle. Dr. Ted Eisenberg, Board Certified Plastic Surgeon and Author. RealSelf Distinguished Hall of Fame Inductee. Philadelphia, Pa., USA