I am huge on black, but I wonder if this is the right place for it. You may find the green gives you a more delicate look. Spread out your sashing fabrics and lay the blocks on top, that way you can audition the sashing without cutting first.
I saw one of these quilts all done up where the bouquets were all pointing in towards each other, the flower part kind of make a big circle around the points, very pretty and an unusual setting, (at least to me).