Scrotal tissue does play a role for depth when you get vaginoplasty, but there are workarounds when there's lots of shrinkage or not much there in the first place. Among other things, you can use skin grafts from the upper thigh or belly, there's a few surgeons that do a technique known as peritoneal pullthrough (you'd have to look up if your insurance covers that, though, it's kinda cutting edge when it comes to vaginoplasty) and some even graft buccal tissue, that is, skin from the inside of your cheek, to line the vaginal cavity. You do not depend on having lots of scrotal skin for vaginal depth, but it does make the surgery easier and has less chance of complications during recovery.

Whatever you do, i can recommend researching surgeons a lot and to get an eventual orchi at a place where you'd also do a vaginoplasty. That will mean that if you change your mind, the surgeon will have done the orchi in a way that does not interfere with their technique for vaginoplasty too much. Also, if the main reason you want an orchi is not "i want to get rid of my balls, but keep my girldick", but "i want to get bottom surgery, but a full vaginoplasty scares me", it's probably in order to think this through a bit more. I really recommend to go with what fits your sexual wants and needs and the way you see your post-transition body, not with what seems the easiest way. That can be either orchi or vaginoplasty, but it should be a decision you make based on what you really want to have in your pants.