I figure since I have a jeep, with square eyes, I need a cool place to work on it. I'm looking for pros and cons of Window units versus Mini-Split.

Details-
The garage is about 400 sq feet. Block on two walls (shared with house) 2x4 construction insulated R13 and 1/2" drywall on the other wall (this wall does not see direct sunlight). The garage door is insulated. I haven't insulated the ceiling yet but will either before or shortly after the A/C is installed.

BTU?
I'm thinking 24K. But I'm being told 12K would be enough. Should I compromise and get 18K?

Has anyone installed one of these mini-splits? If so, can I get some feed back.

TIA