If you press Enter, it will generate one certificate which will be shared between all 16 sites.
My personal preference is to group related domains into individual certificates. So, one certificate for shitouttaluck.co.uk
& www.shitouttaluck.co.uk
(7,8
+ Enter). That way, you don't have problems when you want to add or remove domains.
Realistically, you can do whatever you want.