I don't believe 8 GB will be enough. I've got BT5 32-bit gnome running in a 20 GB virtual machine. I did a df, and I'm showing 40% disk in use on filesystem /dev/sda1. If my math is right, that equals 8 GB...right at your SSD capacity. My BT5 install is pretty vanilla (nothing extra on there). I'd say you need a minimum of 10 GB to account for swap space, updates, etc.