I would stagger the border seams, they will not be noticed when attached and quilted. And, to answer. (Citrus county quilter).....when adding multiple mitered borders the borders are often stitched together then added to the quilt. The measuring does not change, other than you have to add the extra to form the mitered corners. If you are perhaps going to have (3) borders, like a 4" wide, then a 1 1/2" wide, then a 6" outer --the 3 borders would be sewn together into one unit, generally when mitering the corners you need the length of the quilt plus the width of the borders on both ends plus a bit extra for forming the miter, which is trimmed off when you do your miter. It is much, much easier to miter the (3 border unit) as one unit than to try to line up each one individually, when you do them all at once they automatically are lined up with each other.