A few things to consider when sending a quilt out for Long Arm basting only.
1. Using a high thread count sheet is not a good idea. Since the basting will be removed, there will be needle holes. The Long Arm will use a much thicker needle than a hand quilter.
2. Batik backings are a higher thread count than typical quilting cottons. Having sent many many quilts out for Long Arm work , I always ask for my trimmings back. Those trimmings where the long arm pattern extended way past the quilt... the backing trimmings were not usable where the machine had "needled" the area. The holes from the needle were sizable enough that it was very visable and permenant. If it is a basting only this should be minimal.
3. Do ask to have the edges basted as well. Something to consider as well .... , it would be easy for them to make the first trim for you removing the excess backing and batting. I always do a final trim before putting the binding on the quilt.