Choose a stitching pattern like straight rows down or across the quilt to stabilize the layers. If that works well, rotate the quilt and stitch rows the opposite way. It is best not to have to change directions when SITD as you have to rotate the quilt sandwich. Try a test sandwich to see how big your stitch length needs to be set at the get a nice stitch through the sandwich. A walking foot or dual feed on your machine will help move the sandwich.
How are you going to bast the layers before quilting? Pins should go every 4 - 6 inches, or you can 505 spray bast or thread basting or.....