I have been wondering if I need to buy any extra fans for my cooling system. There are a few fans that come with the case i'm purchasing and a stock fan that comes with the cpu. I don't plan on overclocking since I feel it's too risky for my first PC build. This is for a gaming PC.
One fan for in and one for out is enough. What's important is that you want to keep the airflow in check. If you have two 120mm fans taking air in. It would be good to have two 120mm fans taking air out. Extra fans are not really necessary.
If you worry about cooling then get an aftermarket cooler for your cpu. Intel's stock coolers are awful for the lifespan of the cpu.