Opinion on my first build?

I would get Windows 7.
Is your power supply 500W? It will work but if you want to do SLI or Crossfire you will likely need more.
It looks like you've chosen some good parts but one place the vast majority of builders can save money is the motherboard.
I couldn't find the exact motherboard you listed but I'll give you an example.

Gaming motherboards that were considered high end when i was looking to buy a new one were from $149 - $300. My motherboard cost me $65 and has solid capacitors and plenty of overclocking ability. In-fact my computer is overclocked right now. I game on my computer everyday. My computer hardware knowledge helped me to choose an inexpensive motherboard that still runs great.

Too many people don't know what to get in a motherboard... Just know this. All you need a motherboard to do is provide the features you want. So if you want USB 3.0 that won't be hard because most new motherboards have that. The same with things like SATA III and multiple PCIe ports. My motherboard has one (PCIe port) by choice, not because I couldn't afford it. But because I knew I would upgrade to a new CPU, RAM and motherboard before I ever need more than 1 video card.

Chipsets; some might allow you to have 6 USB 3.0 ports and 6 SATA III ports while others may only have the ability to provide for 2 USB 3.0 ports and 4 SATA III ports. The features the chipset is capable of providing are the only differences in chipsets. (Some do allow for better overclocking though.)

If you can't seem to find a cheaper motherboard and you feel it's the least you are willing to get. Then take a step down in the video card department, you can (sometimes) save a lot... I know it's rough to think about possibly less FPS in games but my 7850 can play pretty much any game maxed out at 1080p and thats a couple steps down from your choice. Also, as a couple years go by you can always upgrade your GPU fairly easily. Who knows, in 2 years you might want that 9870...

Lastly, look at the tomshardware main page. For an article about myths about video cards to learn something I've known for many years. The amount of memory your video card has typically has little to no bearing on performance. If you can save a decent amount going with a 2 GB card instead I would recommend that... If the difference is only like $10 then don't bother with the card that has less memory. Personally I would have bought a 1GB card but I found an amazing deal on a 2GB card that was overclocked which was cheaper than the 1GB card.