I love this pattern, and I love your quilt. It's just stunning. Not too many hand quilter's will choose stitch in the ditch. I think that's more of a machine quilter's technique, because if you're going to hand quilt you want the stitches to show. If it was me, I'd 1/4 inch quilt it inside each diamond piece of the star and around each leaf, stem, and flower.
It seems like hand quilters do cross hatching for back ground, and you could do that. You could design a long slim feather motif to fit between the flowers as though it were a bit of quilted greenery in a bouquet. You could do a close Baptist fan motif as a back ground, oriented to cross your flower stems in each of those blocks. It would break at the quarter inch quilt line for the stems and flowers, but from a distance would create quilted scallops around your center star.