Actually if you do not plan on overclocking it then don't even bother getting a water cooler.
Just get an after market heat sinc fan, that is big and has low rpm's so it'll be quiet and cool.
2. No need for a network card, most new motherboards have them built in.
3. Just pirate an OS. It'll save you money, and I could send you my legit copy of win 7 home premium.
4. I would suggest getting two GeForce GTX 780's then use an SLI bridge to connect them. They are both single cards with about 4GB of video memory support Direct X 11, and have vertex shader at like 5. Then combined thats like 8GB of video memory. Or get two HD radeon and use the firewire (or whatever the hell it's called) as I think your motherboard supports it.
So just do that and you could build it for around $800. Save a few bucks, and build it yourself without the water cooler. Search around, maybe not on newegg. But just look around.