First, I love your quilt so far. I quilt with Thermore batting, which says to quilt it every 10". I would begin by ditch stitching and stitching over the stay stitching. That would actually be enough, although I would probably quilt a flower in each of the quarter circle ("pie") sections and perhaps 1-3 leaves in the opposite corner. Of course, now that I know how, I love free motion quilting using the embroidery/darning foot of my machine. There are too many quilts in my life to hand quilt, although I admire those who do it.