Hi,
If you use a fan for enclosure (whole circuit) cooling, define for yourself what temperature is the 'wrong' temperature and why you believe it is, and where it is best placed for most effective results.
You really ought to do PD calculations for each part that may get very/too hot and affect nearby component functionality or reach its own maximum junction operating temperature (or stuff that might melt - improbable, but still...). At least rough calculations. You may not need one at all or really need one on at certain moments.
Fans go well with a hysteresis range to avoid annoying constant on/off behaviour, such as on at 50°C and off again at 40°C or whatever, making the circuit larger, unless the fan is on all the time.
Fans have a cubic feet air flow parameter I didn't understand with first two I bought but is important when comparing products (in case you hadn't noticed that aspect).
They are a good feature to add when you have the additional current to spare but only if really necessary, imo.