Addressing your comfort concerns:
There is R-37 in the walls and R-58 in the ceiling. The horizontal 95% Trane (of course) brand HVAC system is in the garage attic. Direct vent to the attic front wall.
If you look closely you will notice the summer / winter set up in the supply ducts and the returns are in the ceiling.
I upgraded the low pressure natural gas supply from 3/4" to 1 1/2". With three HVAC systems for the main house, new in-law addition and the garage I wanted to have a healthy margin.
The 18' over head door was replaced with a 10' door and extended side walls. The 10' door was subsequently replaced with a 2" X 4" core plug door caulked in place over foam strips for a clean future removal. T-111 on the outside former door space.
I built a 12' X 16' shed for the lawn equipment. The cars and boat stay outside.
The black paint patch on the floor was for backing in my off shore race boat. It would only fit if the tires were on the paint.
Finding a way to close off and seal the garage door was pivotal.
I pushed the garage enlargement to 1 sq ft less than the maximum allowed. The extra single square foot was use for the concrete piling to support the passenger station. Code enforcement smiled and signed off on the project. Net result was an extra 20 sq ft for the RR for 1 sq ft of ground.