Need advice on upgrades

Hey  

Your power supply should be adequate, but this will depend on what graphics card you get.
That CPU will use slightly more power than the E6700 (the 3570k has a max TDP of 77W compared to the E6700's 65W), however i dont believe this will be a problem. the best way is to use the power supply calculator, enter all the information (the graphics card you want to get later down the track is important) and see what it recommends: http://www.extreme.outervision.com/psucalculatorlite.js...

Your graphics card is the main thing holding you back, and i would upgrade this as soon as you can. take a look at this graph.
http://www.nvidia.in/content/product-detail-pages/gefor...
Even though your current card is in the 500 series, it performs less than my 9600GT, which was released in 2008. This is often confusing to consumers, i have had heaps of people ask me to build them a system with what they consider to be a newer GPU but it actually performs worse than their old one. (Ill explain, sorry if you already know): For example, with a gtx 670, the 6 refers to the generation, and the 70 its performance bracket. Generally, 10-40 is entry level, 40-70 is performance and 70-90 is high end. so for your next card, make sure (for gaming) that it has the last two numbers of at least 50 or 60

In regards to CPU cooling, you dont need an aftermarket cooler if you do not intend to overclock. The stock one is fine if you are leaving it as it is out of the box. If you want to overclock later, then go and buy a decent cooler when you need it. this can save you some money in the upgrade if you dont really need the cooler.