I'm not trying to argue here, my opinion isn't just formed off reading on the web. I own my own PC shop and have done multiple installs and more often than not mixing and matching RAM has lead to strange and usually irritating errors/BSoD's etc.
I'm not saying you can't mix and match, I'm saying it's not a good idea generally speaking. Especially not if you are buying an XMP matched kit. XMP won't work if you mix it with other ram.
Good idea, I can REALLY recommend the Seasonic Range of Powersupplies. The M520 is a particularly good psu as it's semi-modular Bronze rated for efficiency and not badly priced. I believe that unit has 3 years warranty.
http://www.sybaritic.co.za/store/product_info.php?cPath=73_269&products_id=67729
Seasonic make argueably the best psu's in the world and most high end Corsair PSU's are rebranded Seasonic's.
P.S The Corsair unit isn't bad, it's just that the Seasonic is far better.