I would change the layout and put kneeling D in the center because it is the only single. Then I would put D with wheel in two opposite corners and D with hands out in the other two opposite corners. Marvel stone blocks on each side and D with wizard top and bottom center.
Then I totally agree with the red sashing. It would really pop the blocks. The corner stones could be a beige or even a gold/deep ochre tone from the blocks.
It will be beautiful no matter what you decide.