You are probably going to want to pull air in from the outside and from below the height of the GPUs then exhaust it back to the outside above the GPUs.
To figure out how powerful of a fan you will need, plug in the heat load in Watts (basically the at-the-wall power consumption) and the temperature rise, delta-T, in degrees Celsius (assume 20-30C) into this equation:
CFM = (1.756 * Watts) / (delta-T)
So, for example, 2000 W with a 20 C temp rise allowed will require a minimum of 175 CFM. That's the ideal case, of course.
Apologies for the mixing of Imperial and Metric units, but using degrees F makes the equation cumbersome while converting from cubic meters / second to CFM is relatively easy.
So help me out here
I am not sure what the "Temp Rise" will be...
But we are assuming 3000w (4000w+ eventually), in a 48"x48"x80" tent. I was planning to run an exhaust fan ducted out of my garage at 700+ cfm, pulling in cooler air from the bottom vents at the floor of the garage. Do I need that much? And would the negative pressure collapse the tent?
Here is the tent: https://www.amazon.com/gp/product/B01M9E10HP/