From everything I read, I thought would be able to boot to the BIOS without the CPU or RAM and do the BIOS update, then plug in the CPU, RAM and SSD to do my Windows install.
As you have pointed out it looks like I needed the CPU and RAM for the BIOS to display.
I didn't want to install the CPU before updating the BIOS because I knew my i7-7700k would be supported.
In the end I did the EZ flash from USB, then installed the CPU and RAM to get to the BIOS then added all the other bits, before putting it all in the case and finally installing Windows.
Thank you very much for your advice, I hope this helps others too.
Craig