I think the fabric you have chosen is perfect for a OBW (One Block Wonder) and wouldn't change a thing. I personally prefer the placement without sashing as it lets the colors flow from one to the next, but using the blue between will give an entirely different look and I like that too. I would suggest finishing your blocks, then placing them on a design wall so that you can stand back and see if it pleases the eye one way more than the other. I think a OBW looks much better from a short distance, much like a blooming 9P.