While Microcenter typically has excellent deals on CPU/Motherboard combos, their prices on everything else are the same as competitors or higher and you're going to be paying 6% in sales tax. Since you said you live in the Philly area, I'm assuming the Microcenter you're talking about is the one in St. Davids. That means the Tiger Direct store in Christiana, DE is also within driving distance if you have a free afternoon and there's no tax there. I'd definitely check them out too if you're adamant about going to a brick and mortar store. If you're OK with mail order, look at Newegg. They often have the best deals anywhere and are highly reputable. The downside is waiting for your parts to arrive.
Intel vs. AMD: In an general sense, yes, Intel is better while AMD is cheaper and there are some people who will never buy AMD. However, AMD does have its advantages in your price range. An FX-6300 is 6 cores and easily overclockable while a Core i3 is effectively 4 cores and does not support overclocking. (An Intel chip with a "K" after the number indicates an unlocked multiplier which makes overclocking easy; none of the i3's are "K" models.) That's not really a big deal right now as most games use only 2 cores, but looking to the future there are more and more programs that utilize multiple cores and overclocking can extend the usable life of an obsolete chip.
PSU Wattage: There's some significant disadvantages to skimping on your PSU, and for the little extra money 600W is worth it over 500W. Most of them operate at peak efficiency and idle fan speeds under about 50% load. Anything over that will dump more waste heat into your system and the fan will run faster and noisier. A typical budget gaming computer draws about 300-350W depending on what CPU you go with, so you're looking at a 600-700W PSU for cool and quiet operation. It'll also pay for itself in reduced energy costs, and PECO is expensive![]()