Insulate it. If your using a ducted AC, itll exhaust hot air into the garage out of the grow room. The ambient air temp of the garage is going to get real high (unless your exhausting more hot air out of the garage as well). Insulating it will help alot if the garage temp gets really high, and keep the grow room cool. Or unless your using a mini split AC and the compressor is going outside the garage.
Im not a pro on the subject but if your using a ducted AC, I dont think a 9,000 btu AC is going to cool 4,000 watts of lights with adjust a wing.
Right now Im in an 8x4 tent, 3-600W adjust a wings, 14,000 btu AC. I have the ducted AC running out of the tent but not exhausting out of my garage, it gets really hot in the garage. Up to 95 on a hot day. I had to turn all the 600W lights down to 400W and my max temp in the tent gets to 84 still. At 600W each the tent gets to 90 degrees +. If I leave my garage door open all night and let all the hot air expel, the temp is fine. But I still dont think my AC could handle another 2000W(even with the garage door open).
If you are using a ducted AC, use something to raise it up high off the ground. That helped me alot, it used to just blow cool air under the canopy and never circulate around the lights where the heat really is.