As much exhaust as you can stuff in there. Don't even consider cooling until you've done all that you can with the exhaust side. Then, if you want to run AC to drop the miner's intake air temps, so be it. I'd recommend an evap type of cooler rather than an air conditioner, far less amperage diverted.
Ive been looking at dual zone split acs they have a rediculous 22 ser rating can cool up to 24k btus and cost only 2300 or so.
wattage is 1600 very reaonaable and you can get a heating and cooling model which helps with humidity in the winter.