Agree that an external HD is the way to go for storage. Partition it when you format it so that you can use SuperDuper! or Carbon Copy Cloner to boot your computer if your internal HD has a problem. You can use the same external HD for the Apple archiving software "Time Machine".
Make sure you look at the June 2012 models. They have USB3 which is 10x faster than USB2. They also have the proprietary Thunderbolt port which is 2x faster than the USB3. Make sure your external HD will work with these ports.
Also, look at the Apple Refurbished list for better prices and the same warranty. Keep in mind that the Retina Display models cannot be upgraded but the non-Retina Display models can be and take up to 16GB of memory, available from Crucial for about $100.