You could do straight line diagonal quilting in most of it and then in square blocks do something like a ginko leaf outline (if that strikes your fancy). For the border, you could do something like sashiko type strait line quilting. Because the spacing in sashiko is longer than traditional quilting, black might be a possibility. But a gray or even the dark red in your fabrics would work and not detract form the gorgeous fabric and your peicing. Just a thought.
I love your quilt top. The finished quilt is going to be beautiful.