Welcome to the board. I agree that you may have trouble with the quilting if you have denim on the back and quilt over the block intersections. Every seam you cross means you are going through at least 3 layers of denim (assuming you have pressed the seams open) -- the intersections even more. Sewing machines do funny things when they try to sew over those big clumps of fabric -- some of them get bogged down, some jump over. With the denim top you need to reduce bulk as much as possible for the rest of the quilt.
That said, I think a nice all over grid pattern (for me it would be on the diagonal) would be nice. If you do free motion, moving a heavy quilt can be really hard on you. If you do a grid pattern with your walking foot the machine is helping you move the quilt around.