Unrelated but for best performance I would use on the non SMR disks (EFRX) for parity, of course it will only make a difference when writing to a non SMR disk also, but like that it can be slower even when writing to one.
It wasn't assigned before rebooting, looks like the clear was canceled, so it was never really assigned to the array, I have no idea what could cause this, never seen it before, best to create a bug report, add both diags again.
You can use this to see usable space.
That is unrelated, it depends on the settings, use cache must be set "Yes" (or "Prefer") and the minimum free space for both cache and share need to be correctly set.