I've resisted the urge to show you all the rejected possible layouts I contemplated before deciding on the final layout (which I'm sure you will appreciate).
In the end the deciding factor regarding placement was the block contruction - 4 patch, 9 patch, more-patch or other (like the slashed ones). Then once that was settled, the accent grey and red were distributed, as well as the strong green fabric. The rest of them just fell into place like good little blocks do.
I binned the modern circle (which I did like) and the string pieced block (which I didn't like so much) as they didn't fit well with the other blocks. By that stage I also knew I needed to add a block which wasn't a 9 patch, didn't have grey and wasn't strong blue.
Now is this one an Ohio Star?
And the friendship star- with a variation in the corners. These were added by luck when I found some triangles I'd cut previously that just happened to be the right size. Bonus!
I've started adding white sashing, with a grey cornerstone. Very calming.