Will you have enough fabric to do B without piecing the top/bottom border? 36" + 4 + 4 = 44" If you are going to straight line quilt it, it really shouldn't make any difference. The seam will look like another line of stitching.
I would put a small (1") dark border on first to contain the colors in the quilt. With the yellow background and a yellow border, they will appear to bleed together, unless you want the cats to look like they are floating in the yellow. I would also quilt the corners with a diagonally.