Hey,
I was looking into doing something similar to that myself. I am leaning towards just setting up an addition box rather than an external drive. With the seperate box, you can have it connected to your home network, being more easily accessed by other computers. Its also handy because you can set up an file-server on the box, so you can access them from alternate locations.
Just an idea. Let me know how that external drive works out for you, if you do it. I might change my mind to that myself.
~jinsta