The size of the design dictates how the design is going to be digitized. A large design, with a lot of open ares would have to be complex fill stitches. A small design could use satin stitches or steils. Size is pretty important. I know what you are saying about vector files having no definite size, however, you are still viewing the image at a certain res due to your monitor and if you try and digitize a very large design from a low zoom, you will not be as accurate as digitizing from a higher zoom 3:1 4:1 or even 1:1 on a smaller design. Do you have some digitizing software? If you do you can use that to size it to what ever you want, but there again adjustments to the design will need to be done.