It's impossible to say what 720 cc expander will equal in a bra size - as it's not designed to be a breast mound, just a place holder. If you are happy with the general appearance of the breast mounds then you are done filling and are ready to let things settle. When you next meet with your plastic surgeon discuss your implant options and your desired goals. They will be best able to match an implant to your anticipated result.
I always ask my patients at what point during the expansion they are happy with the volume and then go from there. Bras do not match up with volumes of implants.
It looks as though you are making good progress. Please discuss your size questions with your plastic surgeon, who knows you best and can advise you. Do not get overly concerned with bra cup sizes, where there is a great deal of variability. Instead, look at the mirror and ask yourself if you would be happy with this size. To my eye you look proportionate and well balanced. That does not mean that your personal preference might be to be a bit larger, or a bit smaller. There are no wrong answers. Sometimes different implant sizes are necessary to off set any asymmetry in your native breast tissue envelope and your plastic surgeon will make that determination before or during your surgery. Best of luck with your ongoing care.
Based on your photos, I agree you have plenty of expansion and should not need any more. The final implants will not project as much so be prepared for feeling smaller. If your goal is to have a natural result, also discuss anatomical shaped implants with your surgeon. Also make sure they move the final implants toward the midline so you do not have the feeling of implants in your armpits. Good luck!