1. The stock HSF is fine, even for overclocking. Don't feel that you have
to change it.
2. Unless you have one of those dumbazz cases with the bottom mounted power supply, all you need is one 120 mm exhaust fan in the rear of the case. Front intake fans are of very little benefit, side panel fans are disruptive & should NOT be used. Also, removing the side panel renders the case cooling fans ineffective.
Have a look at this:http://tech.icrontic.com/articles/pc_airflow_heat_cooling_guide