Hi, welcome. The main difference between regular saline shells and expander shells is the (remote) valve that in regular shells is designed for single use and with expanders for multiple uses. The regular shells go up to 800cc (unless custom order for bigger) and have been overfilled in the past by 500% or more. Meaning they have been succesfully used up to 4000cc. Not only that, but there are surgeons willing to fill up the same implant multiple times through the same single use valve. They’ll want to have a new set of implants standing by in case the valve breaks (since it’s obv. not designed to be re-used), but I guess it goes well a lot of the time.
Expanders are somewhat easily available up to 2000cc shells, which then can be relatively safely overfilled up to 300% for about 6000cc. Know that with expanders the chances of complications and infection go up quite a bit as well as the cost. A surgeon can give you some prices (for instance Dr. Domanskis).
With your “modest” goal of 1400cc I wouldn’t even think about expanders at this stage. It’s easier to have that last surgery go as big as you can in case you want more and if you ever decide to wanna go lets say way past 2500-3000cc, maybe then consider going the expanders route.