If the quilt is going someplace specific, like a bed room to coordinate with decor, I may buy it all at once. Usually, I either make the "insides" and see what border it wants, or start with the border fabric and coordinate inward. Again, unless I want it all 'matchy-matchy', I leave the backing go until I'm finished. I've started doing a lot of pieced backings, becasue they are so much more interesting, and I may have fabric leftover that can be used on the back.