Thinking of fitting a second (1TB) hdd and was wondering will it / can you make it mount automatically or will I have to mount it every time I want to read / write?
The partitions on my laptop (dual boot) are seen as separate drives and have to be mounted every time I turn it on.
To mount a drive at bootup… just add the partition(s) and where you want them mounted as an entry in /etc/fstab.
Note: Backup fstab first though 
To get the partition(s) UUID, run:
blkid