For the intended use you don't need nearly as much as you plan on buying. Most games are GPU based, and most games, even those that are more CPU based, only use one or two cores. And surfing the web is not even an activity worth mentioning when you build a machine like that. You could easily make do with something along the lines of a i3-3220 (dual core with HT) and the very first B75/H77 board that fulfills your requirements.
Which brings us to overclocking. You may have gathered as much by now, but overclocking is simply the possibility to increase CPU frequency quite a lot and boost performance in a noticeable way. With Intel this means, as already pointed out, buying a "K" CPU, and Z77 board, to put things simply.
You don't have to look at it as boosting a system you don't need to boost, but more as a way to "upgrade" that system later down the road with no expense but a little of your time and patience. The same thing would apply to crossfiring that GPU (adding a second, identical card) : probably not something you'll need right from the start, but it could come in handy later down the road too. If you plan to stick with that Radeon GPU, there are good news : Crossfire X is a feature fully implemented in "cheaper" Intel boards, whereas for SLI you usually have to take it a notch or two closer to "high end" boards, within a given series. You could easily find a board that supports Crossfire X, but not overclocking, for less than 100$...
And then there's the future... as much as a CPU the likes of the i3-3220 on a basic board supporting Crossfire X will probably hit a sweet spot for you now, it may, or may not, quickly become a bottleneck in the future, when games will use CPU capacities more extensively. Some already do, as a matter of fact. So quad core is not a bad idea after all, and the thing is, if you're to spend some 160$-180$ on a i5 non-K, then the gap to the i5-3570K is not worth the savings. And it so happens that the board you listed does support all what's needed, so it really just comes down to investing a little more on the CPU - as was already advised, too.
I like the PSU. While I agree that a 450W-550W PSU would be more than enough to support a single graphic card Intel system, there are other benefits that are often overlooked. The first being, you just never know what you're going to add in the system later down the road, like a dual graphics cards setup. Even if you THINK you won't need it NOW, it's only when you'll start using your new system that you'll know for sure what you need. And usually, using a new, better system than what we had previously does lead to doing more and more things than we thought we'd ever do in the first place. On top of that, they usually cost like 10$-20$ more than their 500-550W counterparts. Another benefit of bigger PSU is more cables, more connectors, and hence easier to manage when building, and easier to upgrade in the future. You may not need the 150W more to power up that extra HDD you'll buy six months from now because you'll have decided your computer is to become the media hub of home entertainment... but you may very well need that free Sata connector on that loose cable at the right place, because the other ones are already tied up in such a way that you just can't undo it without having to reconfigure the whole damn cable management.
With all this in mind, your components are perfect, except for the CPU, you should definitely go with the 3570K.
