Upgrading, please critique

Hey guys, I'm am looking to upgrade/completely rebuild my computer. I want to be able to play more modern games than I can now. I'm thinking about basically doing a new build and using my current computer for browsing the web and other small things...

I already have a decent GPU and PSU (PSU, GPU). I plan on getting another 4830 after I do this upgrade and setting it up in crossfire with the one I have. Will that PSU support two 4830's in crossfire? Is that even a good idea? You think I will be able to run Crysis with that (and the new upgrades below)?

On to the new parts...
HDD: WD Caviar Black 500GB
CPU/Mobo: Phenom II 940 and Gigabyte 790gx
Memory: G.SKILL 4GB DDR2-800 Should I go for DDR2-1066 or is it not worth the extra $10?
Case: Antec Three Hundred
OS: I'm a student so I downloaded my free copy of Windows Server 2008 and I will enable everything so it is basically Vista...

The reason I chose that mobo is because of the Southbridge. I have heard that the SB750 is great for the Phenom II's when it comes to overclocking... I was thinking about a 790FX because it does full x16,x16 whereas the 790GX does x8,x8 when in crossfire, but I've come to the conclusion (after reading many a thread) that there is not a noticeable difference...

Let me know what you guys think. Keep in mind my budget is about $550

Also, is it difficult to do a crossfire setup? I noticed there are two "sets" of pins on the top of the card and crossfire bridges seem to come in packs of two. Do you connect both of those, or just the front or back? Is a setup as easy and plugging in the cards, connecting the bridge, getting the drivers, and enabling crossfire in CCC?