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.
If you run in the room itself also you need to exhaust and air conditioned for it bro. There is no heat issue will be produced if there is good temparature in your room bro. I see you are recommending big estimation for running with the high cost of electricity already with the miner.
Garage such a hot place. If you add the EVAP coolers are heating in the roof means it still as very bad temparature.
My electric cost is very low. Why would I spend 10A on an air conditioning when I can spend 2A on an evap cooler and use the other 8A for miners?
Ambient outside temp here reaches over 36c for months. The evap cooler allows me to keep miner rack air intake temps under 27c which allows me to run the cards hard but they stay under 70c.