This is my first time building a system so any feedback would be appreciated.
Do I need any other parts? Should I change anything? Will they work together? Will it all fit in the Antec 902 Case?
I was unsure about how big a PSU I need? I put down an 850W, but could I get away with 750W? Is there any other place I could cut down in cost?
I was also confused with the different types of Memory. Any recommendations?
Since you are mainly doing video editing, you will benefit from the additional memory that the ATI cards have, not to mention this ATI card has both DX11 and ATI Eyefinity, and is $50 less than the card you chose.
Cooler: Coolermaster Hyper 212. One of the best, it's also one of the cheapest. It's not huge, and it will fit any socket.
Mobo: Spend a little extra and get: ASUS P6X58D Premium for $300. It's more future proof, and you really don't need to have the ability to Crossfire (yes, Crossfire) 3 cards. It doesn't work very well.