We've installed ductless mini-split heat pumps in at least two garages (coastal VA.) They are a great candidate for space conditioning a garage, in my opinion. The size of the unit required will depend on the climate zone, insulation, and amount of air leakage in the garage.

An thru-wall, integrated unit would seem to be much easier (and cheaper) to install. Example:

• Koldfront 8,000 BTU 115-Volt Through-the-Wall Air Conditioner Cools 350 Sq. Ft. with Heater and Remote in White
• Koldfront 26 in Metal Through-the-Wall Mounting Sleeve

It might not get cold all that often in Los Angeles, but any HVAC design needs to consider both the heating and cooling needs. The 2018 IPC cooling/heating design temperatures (2.5%/95%) for LA are 80 F dry bulb/69 F wet bulb and 43 F winter dry bulb. A heat pump will provide both cooling and heating and would be the better choice to maintain comfortable conditions year 'round.