I post this for those like me whose PC was not powerful enough to play this when it came out and had to suffer through it on Xbox or PS3. Also great for those who never bothered to get the DLC.
It's a 12 GB download and 24 GB install. Amazon download speeds are not as bad as I thought they'd be, either: 3-4 mb/s. I believe you can use your activation code through EA's Origin service and download it from there if your Amazon download speeds aren't great.
During the installation process you'll be asked to enter your activation code for DA: Origins which can be found at Amazon in your games library, but when it comes to activating DA: Awakening and your other other DLC it will take you to the EA/Bioware website where you'll have to enter a separate activation code (also found at Amazon), that will require you to have an EA/Bioware account. The DLC can also be activated in game through the Downloadable Content section on the title screen which, of course, still requires an EA/Bioware account. As if that wasn't enough, when you first run the game you'll be asked to enter your EA/Bioware ID to activate the game for use on your computer.
So, if you're willing to go through that DRM nonsense, enjoy killing those dastardly Darkspawn!