Personally, I would clean out some of the TV shows and movies, not like you can really watch them while driving
As far as the drives we us the laptop drives which use less power and produce less heat, though one on USB as a removable and be done with it. when that one fills up, upgrade to a larger one.... USB disks are growing fast in size, I just saw a 20G usb disk!!! maybe wait till they hit the half TB and use one of them