I used two 12"x12" Doran lightproof darkroom vents in my darkroom build. Where the vents were going to be installed, before the sheet rock was installed, I framed a 12"x12" box to hold a common 12"x12" furnace filter. On the outside wall I installed metal vent covers that are removable to be able to replace the filters easily. The darkroom door seals almost airtight, making the filtered vents the only air source. I also installed a quiet exhaust fan connected by a flexible hose to a length of plastic pipe with holes drilled into it at regular intervals that runs the length of my darkroom sink (10') and sits under a shelf. Result: good ventilation over the sink, which is replaced by filtered air through the vents.
I also have a filtered electrostatic cleaner to remove any dust that does sneak in; it just circulates air.
Maybe something similar will work for you.
Best,
Doremus