108" square is a *large* quilt! You may want to divide the batting into sections to make it easier to handle, especially if this is your first quilt FMQing.
Have you practiced FMQ on practice sandwiches? If you are planning on a "squiggle" type FMQ, then people usually do not mark. If you are planning to FMQ a specific design, such as a flower motif, you may want to mark the design on the quilt top before starting. Marking in itself is a major subject for a separate thread (no pun intended!).