A half related question :

While SD cards are awesome for size/weight/etc., how much of a speed advantage would using an external hdd be? I can't imagine an ssd adding any value over a simple 2.0/3.0 mechanical drive being that the transfer rate is bottlenecked by the shared usb 2.0 bus which apparently is divided up by the all ports and the sd card reader. Is a top of the line sd card just as good as an external hard drive or are there any advantages?

@doctorstork This is correct. When you put the SD card in the Pi for the first time the root file system is automatically expanded to use the full size of the card. This is free space and can now be used for storage. Go into the terminal / command line and enter df -h this will show you how the card is being utilised.