Looks like a nice system - you should be good to go. I'd personally add a Hyper 212+ cooler as well. (Or another CPU cooler - the stock Intel one is fine, but you better overclock if you're buying the K version of the 2500...)
And I would go with the samsung f3 from amazon for the same price as that seagate drive and don't worry about it not being sata 6.0GB/s second because mechanical drives can't even saturate a 3.0GB/s connection.
I have one lone suggestion. A different case.
Don't get me wrong the challenger is an excellent case, I've used one. However I would get the HAF 912: http://www.newegg.com/Product/Product.aspx?Item=N82E168... It's a bit roomier, and has much better cable management. My biggest complaint with the challenger is no room for cable management.