Hello, Clemmy Clem.
Does anyone know if the SSD (or any drive you install to for that matter) have to be the 1st available drive?
It should be the drive which the Bios wants to boot from. I.e. if you have got 2 separate disks in your machine, assuming they are /dev/sda and /dev/sdb, and you have instructed your Bios to boot your machine from /dev/sdb, then /dev/sdb would be the right location for Grub.
As a rule, however, the first drive in a machine will be the drive where the Bios looks for a bootable system.