Do you NEED an aftermarket cpu cooler, either air or liquid?... NO.
The Intel stock cooler will work just fine for your 2400 even at high cpu loads.
But, when the intel fan speeds up, it can be quite noisy.
I do suggest the cm hiper212 for $20.
1) The larger 120mm fan will be quieter at all load levels, and it will cool better.
2) The stock intel pushpins are difficult to gat on properly, particularly for the novice.
The hiper212 has a backplate mount that is easier to install, and is more secure.
Lastly, do not worry about overheating. The cpu will downclock itself, or even shut off if it gets dangerously overheated.