re: Shop heating and cooling

dI installed a MrCool DIY mini-split last year and love it but does sort of sound like overkill for you.  Before the minisplit, I used a 12k BTU portable AC with heat function to cool and heat my shop and a quartz radiant heater to boost the heat on the coldest days.  If you go the portable route, you definitely want a 2 hose portable AC unit because otherwise, it will simply suck unconditioned air in through any cracks of vents, reducing the efficiency.  I don't have any windows in my garage shop so I added garage door exhaust vents to route the AC hoses through the door for the external air exchange.  The vents are designed for mechanics to vent exhaust pipes outside for running the car engines while the door is closed.  They were a little small but that didn't seem to affect the efficiency of the unit.  I basically replace the hoses with drier hoses with a quick disconnect connector that fit the door vent.   If you have a window or can cut a hole in the wall, a window unit will be cheaper and probably more efficient but the portable unit is a nice option, especially if you will only use it occasionally.