Yes, there are 2 versions. You can go to its official site and take a look:- www.eset.hk
Yes, they have such capacities, 500G and 1T, for some brands, even 1.5T, the size of the HDD may not be so compact. Ask the retailer.
NOD32 is definitely super!! good interface and strong protection. If you connect to the internet permanently, be sure to use the 'Smart Security' version, not just the 'Anti-Virus' version.
About the USB HDD - take note the USB interface - 2.0 or 3.0 in your notebook - 3.0 is a lot faster!!!!