To add further complication:
Adding an external card will give you flexibility on the amount of data you get to carry with you. The only thing to remember is that you cannot install apps to the external card using stock. All apps will reside in the internal memory without an option to move to external card. There are a few apps (ie. Navigon, Bard's Tale) that will allow data to be moved/installed into the external card and still work. That's because the developer actually took the time to write it in their program.
If you want apps in the external card, you will need to look at rooting the device and using directory bind to flip the internal/external storage recognition in the device.