Just an advice it is good to have a small space for your OS and the data to the bigger drive. I have a 640Gb for OS and program files and I have second drive for my movies and audio files on 808 WD prosperity drive. And I have an external drive for backup 1Tb, 2Tb. I don't always connect my backup only when I need to get a file.
You can have say 500Gb OS + program files and 500Gb other files, 1 external drive 1Tb. Coz if anything happens with the second 500Gb drive you only get it back on the back up.