It'd difficult to give an exact answer because you yourself don't appear to know everything that's needed but I have to make one thing absolutely clear - you do not have 1.2TB to play with.
The reason is that under no circumstances at all would you do anything other than mirror/RAID1 those two boot disks. This will enable you to survive when (not if) one of those disks dies.
Now onto the actual recommendation - buy at least two more disks. Seriously.
The reason is that you should put your OS onto those two boot disks (in a R1 pair) and store your data on another pair (or more) of disks in either a R6 or R10 array. This is what professionals do, it's boring why but it's all about keeping your OS workload off your 'regular' working disks and vice-versa, it keeps thinks nice and neat too for when things need to expand/change/move etc.
So you put your root, var etc. OS filesystems on the first R1 pair and the create a /mnt/data or whatever filesystem on the second array for your actual data.
If you're new to running Linux I'd advise you to take the OS's installation default for the sizes of the various filesystems (maybe extend /var, the defaults are often too low) but user LVM and leave a good chunk (several tens of GB) of free space so that as you come to know how your OS behaves you can shrink and grow the individual filesystems accordingly - if you leave this space unused it makes life that much easier. Whether you use LVM or not on your second array is down to you, it really depends if you can afford the few percent performance hit its flexibility gives you. Oh and don't be afraid of the ext4 filesystem if you're using a modern Linux, it's very stable.