Black border first then the peace sign fabric and bind in the black.
Backing I would go cross ways with the seams. So you could do 2 strips of one color then 1 strip of the other color. Are you having this machine quilted? If so I would say the fewer seams on the back the better it would be. It's a beautiful quilt and many hours have gone into it. I'd love to see a picture of it after it is quilted.