There is no connection between the brand of the graphics card and the motherboard. I don't really know why that MSI card is more expensive than the EVGA one, frankly I prefer EVGA cards to MSI, but that it just an opinion matter.
650 watts is more than enough for a build like this. The only time you really need more is if you're running a lot of miscellaneous internal components, or you're trying to run multiple graphics cards. Since you're doing neither, that PSU will be perfect.
Windows 8 is fine if you are willing to deal with the user interface. You can also get that amended and make it look and feel just like windows 7. And it is a faster OS. But there is still compatibility issues with some things, and you don't really get any benefit over 7.
I still recommend Windows 7 over Windows 8.