Bottom surgery questions

I believe I tagged this correctly
I’m 27 trans and looking at getting bottom surgery. I’m less about debating the option of it at this point and more about the logistics of owning a new…set of equipment. I’ve heard that women need to dilate weekly to make sure their vagina doesn’t get too tight. But can it flip the other way? My gf is large in multiple definitions. But I’m worried I won’t be the right size/depth for her. So is it possible to stretch out a bit more?
Also wanted to know, how much does length affect depth/surgery overall? I’m not a big size as is so I’m worried there might not be enough to work with.