Whatever cable you put in the walls, make sure it is CUL-approved. You may not be able to get your installation approved by the inspector if you don't do so.
Also, make sure you run the cables as far away from house wiring as possible. And if you need to cross any house-wiring, make sure they cross orthogonally.
I second what Robb said about running 7.1 for the future. Forget WAF when running cables. Also, you may want to run sub cables to a few different areas of your room as it's probably not clear to you right now where exactly the sub should be placed.
And Home Depot does indeed have good 12 gauge wire for less than a buck a foot.
