Overclocking is not a horrible idea or anything, as long as you dont overclock too much. You can ruin your processor by overclocking if you are not careful. It is probably not a good idea to overclock if the CPU fan is stock because overclocking makes the CPU run a bit hotter and a stock fan probably wont be able to handle the heat. About the case fans: If they are pushing plenty of air, it should be fine... But if they aren't moving much, it would be a good idea to get a little more high quality fans.