Up your multiplier by a little at a time and see how far your stock voltage will take you.
If your computer fails to post after a certain multiplier jump, you know it's time to bump up the voltage by a little bit.
However, I wouldn't recommend a heavy OC with your motherboard. My brother personally uses it and I feel very uncomfortable that it doesn't have a heatsink over it's VRMs. A slight overclock wouldn't be of much harm though I wouldn't think.
1) I would say overclock through software until you arrive at your stable settings.
Then go back and copy the stable settings into bios once you arrive at a number(or maybe the software can do it for you)
2) Find tutorial on overclocking, it will describe how to do it
Pros-faster computer without paying extra. So if you often run tasks where you wish cpu was faster to process, like rendering or encoding that will be reduced, and your jobs will be finished faster.
Cons-trial and error and work to arrive at stable settings. Computer may run hotter if you continously are at 100% cpu usage and/or have upped voltages or clock and not just multiplier. Potentially it may cause parts to fail earlier due to the higher work. Potentially even when you think you have stable settings, computer crashes or bluescreens randomly and you have to go back and adjust settings more.
Conversely, if you have no tasks which require more CPU, then you aren't needing the extra cpu usage anyway. But at the same time, cool n quiet will also be idling your CPU when you don't need it, and just speed up when you do