As zander said, though you can keep the psu if you want future headroom - it's the gfx card that most folk tend to upgrade. If you can stretch, a small SSD for the OS and a few programs would make a big difference in desktop experience (80-120GB). Not essential though. Not a bad build.
I at most times don't recommend AMD CPUs, but these CPUs beat the hell out of i3-2120 even i3-3220, so FX 4300 or FX 6300 would actually be better and around almost the same Price, they are also overclockable, so you ould overclock them in the future if you get a decent cooler.
Just remember to get a MOBO which fits with AMD CPUs.
Get a 2 GB version Radeon 7850 that 1 GB are going to be struggeling if playing at 1080p.
Windows 8 are a better gaming OS. It requires less performance, which Means more performance in games. Not by much though. The speed of windows8 is also awesome. Booting time takes around 3-5 sec for me, I use HDD not any SSD. So go for that instead, no matter how much you hate the metro system.