Ok so I hope your pc fan doesn't need to deal with a carbon filter, because they don't handle resistance too well.
But for light leaks, look up "light traps" Its essentially a cardboard box or other material, with angled walls inside, black in colour, designed to reflect light back and not around the walls of the box. Literally a shoe box with a couple of pieces of card will do it.
The good thing is it doesn't stop airflow.
As for a tent door just a layer of black and white panda film, or two layers if needed. You could use Velcro to keep it secure.
