I'm about to make a quilt just like this one for my little man, yet to be born. My squares are going to be different prints with teal, light blue, navy, and brown. But the idea is only in my head, I haven't actually planned out any measurements yet. I hadn't thought about what the back should look like, but I LOVE your idea of the patchy border around the white! I was going to do a patchy binding, but I think that might be overkill with the border.
How big is your quilt? What size did you cut the squares? How wide is your sashing?