As for piecing the back, I usually try not to have one seam down the center. I'll cut the fabric in half (for the center piece) then cut the other half in half and piece it that way (so there would be 3 pieces). It's your quilt, so it's up to you! I have also scrappy pieced the backing with quilt top remnants (larger pieces) or coorindating fabric. Then I don't worry about seaming in the center.