Dasha, in her comments asked me if I had tried butting the blocks up together without sashing. I actually hadn't tried that version, so I promptly did it and took a photo to show.
It's certainly a viable option. But whilst I love the little stars the connecting blocks make, it doesn't solve my busy-ness problem.
So...I have made an executive decision. I will sash it with probably 2.5" white strips, and have the blue cornerstones as in my previous post. I'm going to probably make the outer borders out of black, if I have enough. And then I will do what Bonnie did for her original quilt for her borders.
And then I will have all it done. As to what I will do with the remaining green checkerboard fabrics, I don't have a clue. Perhaps I will put those away. I'm not keen to unpick them.
That's my Grand Illusion mystery so far. Hopefully I shall sew tomorrow. Cross your fingers!