ANY air-cooler will do, 4.5Ghz is just lol with an i5-2500k.
If you wanna do 5Ghz however, you will appreciate buying your own TIM and something decent like mugen2 revb or hyper212+ or anything in that performance range.
Buying AsRock lol -> all you want is a basic p67 or z68 board from gigabyte/asus, you don't need anything more powerful for such a small OC.
And no you do not require cooling on the VRM's, for your OC you will probably remain under 125 130 watts and those things are largely specced for that - hell I even run 150+ watts on these without any issues (provided you have a decent case like antec one hundred with good airflow etc.).
All in all, if you plan to overclock, push it, force it, it won't happen naturally.
And more than anything, don't ever listen to those who lack the balls, they'll always tell you "stop here" or "buy this expensive mobo you need it" or "omg you put 1.45v on your sandy bridge that's too much"-> lol official Intel spec you're still under warranty -.
All you need for OC is good cooling and all the voltage tweaking options you can get in your bios, the rest is extra, like 37 phase CPU power.
And if you really think you do need coolers on your cpu power stage, just buy some it costs nothing compared to the price difference on those mobos.