You might want to change the FX-6100 to an Intel Core i5-3350P if you want better game performance. Your FX-6100 will be the bottleneck for many games since video games do not make use of all 6 of those cores. You will also need to find a different motherboard that works with an i3.
The 7850 2gb is a great deal and while I have the Sapphire 1gb version(accidentally) it is extremely good when OC to 1100 core and 1300 memory on stock voltage. Even stock it runs current games maxed fantastically(60fps with v-sync off).
You could save money on the motherboard by only getting the minimums of what you need. Since this is your first time you probably do not have to worry about getting higher priced motherboards when you only want what is needed.(Assuming you wont need a fancy mobo.)
Just btw you can gget a great deal on newegg or ncix with the 7850. For ~$150-160 you can get the 1gb version plus two free $60 games with the never settle bundle. Seems like a pretty great deal. (hell, I'd just buy that as a second GPU and sell the games to get a $30 7850)