1 x round 120mm exhaust = 5x 70mm round holes. intake surface = 2x exhaust surface. Not the surface of filters etc. Just the cutout. I learned that with impellers and it seems to be working here also okay.
Yes, first i had printer in living area and I used intakes without foam. I also liked to block middle intake hole, so there were 4 active. In the workshop I added some foam to those 4 active intakes. I run fan at 10-40% for all materials.