You can safely do LIMITED overclocking with that board. But is has low phase power and no heat sinks on the VRMs. If you want to see what you can get with the multi alone, it's probably OK. But I wouldn't raise the voltage any. And of course, you do so at your own risk.
Your last question, I don't know for sure. So I'll pass rather than give you bad info. But OC'ing the iGPU won't make much difference anyway. And if you have to raise the core voltage, you are back to the problem I mentioned above.
You'd probably be better off buying an Athlon X4 860K and a discrete gfx card if you game at resolutions above 720p.