If you're worried about it not working properly, you may be able to find a local shop with fairly competitive prices and who's willing to put it together for you for a small fee. Also, there's more quality budget-friendly cases around than the one you chose; $80+ is a lot unless there's features in it you're specifically looking for. The Cooler Master HAF 912 Blue Edition, for example (
http://www.newegg.com/Product/Product.aspx?Item=N82E16811119272 ), is $60 and commonly is highly rated.
I would also recommend spending a little more money on a slightly larger power supply. An extra $10 gets you this one (
http://www.newegg.com/Product/Product.aspx?Item=N82E16817438012 ) instead, which is 500 Watts and also 80 PLUS Bronze. The reason I bring up a larger PSU is that even though your currently lineup adds up to about 200 Watts, at some point you're going to want to add a dedicated video card, which can take up a bit. I don't know if you read the review on this site about gaming CPU's (
http://www.tomshardware.com/reviews/gaming-cpu-review-overclock,3106.html ), but they list the FX-6300 at the same price point as the processor you listed. It requires a different motherboard (AM3+ instead of FM2) but you can get a reasonable board for actually less than what the MSI board on your list does - so you should be able to get better performance for less. Oh, and according to
http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107.html a reasonable video card for gaming will be about $80.
Something else I would note is that if you have a dedicated video card, your RAM requirements aren't as high simply because when you don't have a discrete card - ie, you're using the on-chip graphics of your CPU - it uses your RAM not just for regular applications but to handle the graphics as well. A discrete video card like a GeForce GT 640 has its own graphics processor and memory, so the CPU can concern itself with just CPU stuff and not graphics as well. This means you have the option of cutting down to 4 GB reasonably and putting the money you're saving in various places toward an actual video card. If you want I can try and price out a system for you. Leave me a message!