Everything looks good, but the H50 really isnt a great cooler you can get better results with a decent air cooler like the Hyper212+ for cheaper, also unless you are using high end headphones or a really good 7.1 surround then the onboard sound will work fine. This will save you some money to put into something else like a 5870 or keyboard/mouse.
Also I recommend purchasing a USB interface keyboard and mouse for gaming.
I own both of these they are comfortable and works great.
There is nothing wrong with Seagate, I cant speak for Samsung because I havent owned one, but I have owned WD and Seagate and have never had any trouble.
When it comes to HDDs it is personal preference.