So I am building my first PC gaming build, and I have been researching about parts and what are good since February 2013. I am just wondering if I need 500w or 600w for this build. I want to upgrade in the future too.
For a system using a single Radeon R7 260X graphics card AMD specifies a minimum of a 500 Watt or greater system power supply. The power supply should also have a maximum combined +12 Volt continuous current rating of 26 Amps or greater and have at least one 6-pin PCI Express supplementary power connector.
For a system using two Radeon R7 260X graphics cards in 2-way CrossFireX mode AMD specifies a minimum of an 600 Watt or greater system power supply. The power supply should also have a maximum combined +12 Volt continuous current rating of 36 Amps or greater and have at least two 6-pin PCI Express supplementary power connectors.
Total Power Supply Wattage is NOT the crucial factor in power supply selection!!!Sufficient Total Combined Continuous Power/Current Available on the +12V Rail(s) is the most critical factor.
Overclocking of the CPU and/or GPU(s) may require an additional increase to the maximum combined +12 Volt continuous current ratings, recommended above, to meet the increase in power required for the overclock. The additional amount required will depend on the magnitude of the overclock being attempted.
It also depends on what upgrades, whatever they may be, that you're planning for in the future.
Asus's Wattage calculator reckons for your build, with 5 case fans (2 for that cooler of yours, and 3 for the case), that it needs a 500W PSU.
However, these things aren't perfect, and personally I'd go with a decent 600W (80+ Bronze rated), as this gives you some future proofing if you do come to add another video card, or more hard drives etc.
Corsair do a nice 600 Watt 80+ Bronze rated PSU. It's their builder series one, the 'CXM600W', it's semi-modular, meaning you won't have a huge mess of cables in a fairly basic system like yours.