You can go with Windows 8 if you prefer. It should be cheaper (non-pro version) than Windows 7. You don't have a very good PSU. You can go with Antec, Seasonic and XFX PSUs (good Corsair PSUs are more expensive) that are in the 550-650W range. Only go further than that wattage if you have dual-GPUs or 2 PSUs or are over clocking extensively with something like liquid nitrogen or water.
If G Skill Ares (low profile) RAM is cheaper then get that (DDR3-1600mhz).