i just looked at the pattern. If one was using a layer cake, each 10 inch square would be cut into one 5 inch square, four 2.5 inch squares, and four 2.5x5 inch rectangles. At that point, you could choose whatever sized sashing you wanted, but
i would go with 1.5 inches wide. It's relatively easy to handle.
My biggest concern would be which way to press the seams so that they would nest with the next block.