Update on my mini split purchase:
I had the 12,000 BTU Mitsubishi installed a month or so ago. Went with the hyper heat model (only $300 more) with the i-See infrared eye feature. The i-See is overkill for the garage, but it came with the hyper heat.
It got down to 25 degrees this weekend, and the thing is working great. Just thrilled to have heat (and AC) in the garage. Staining a cedar gate, and it's so nice to not enter a tomb. And I haven't even spray foamed it yet.
Thanks to everyone for all of the advice and info!