ventilation

the more the better is the general rule of thumb. just watch out for light leaks

 

Enough to exhaust the heat at a minimum.

Optimally, you want something pulling air in, another sucking it out and some moving the plants

IMO, ventilation and air movement are highly underrated and underutilized.

 

For a clearer answer to your question, some numbers need to be mentioned and some specifics on your equipment and temps. A good start would be cubic feet, lighting, existing ventilation and cooling, etc,

 

I think they say you want to cycle the air every 3 minutes at a minimum. Shouldnt be difficult in a small box.