I vote for staggering the blocks. Sashing will make it larger. The quilt on my design wall has sashing only on the ends of the blocks, not the sides, which adds another element - the white sashing zigzags up and down across the quilt. Because yours is all blue, I'd go with sashing on both ends and sides. That was my intent, but I made the blocks a long time ago and when I found them recently, I had forgotten they needed side sashing and just sewed them together staggered. This was what I intended (the 2nd quilt down).
http://tearosehome.blogspot.com/2011...love-no53.html