I've learned a lot from this post. I think the cornerstones make it easier to match ups since you'd be working with a shorter length of fabric and it would be more manageable.
Finish your block, square it up, add vertical sashing, then add horizontal sashing with cornerstone--and in a perfect world...viola!!!
I LOVE your quilt and have added that on my "to do" list for all of my grandsons (5 of them :) ).