It would be really helpful if you could provide a picture of the quilt. I googled images of a 9P snowball quilt and here is a pinterest link with pictures. Does it look like any of these?
https://www.pinterest.nz/pin/403916660312261230/
Also what kind of embroidery? Hand, like redwork style or machine which is usually very heavily stitched.
Very hard to make quilting recommendations without seeing the quilt. As far as what you need to know to prep the quilt for a LAQ it would be best if you ask your quilter that. I prefer a backing that is at least 10" larger than the top so I have 5" all around to attach to leaders and test for tension. Some LAQ can get away with less and I can too if pressed, but I prefer the full 5" or more.