How to best use LG heat pump in New England.

I had new mini split heat pump system installed this year in a 1330 sq ft apartment on two floors in a 3 apartment house in Massachusetts. Details below. I still don’t know how to run it most efficiently. I often run only the 9kBtu unit in the main living/dining/kitchen room downstairs. This also somewhat heats the upstairs bedrooms, the stairway being down a hall, and with no door to keep heat from flowing up the stairs. Is this efficient? I read that it’s bad to have an undersized heatpump running at full output, but in this case the indoor 9kBtu might be running hard, but the outdoor condenser would be running at 9/30 kBtu or only 30%. I believe the minimum that the outdoor condenser puts out is 27%. Am I better off also turning on the other downstairs study 7kBtu unit, in which case I imagine the 9kBtu would still have the main load, with the 7kBtu unit (oversized for its small room) taking off some load? Or, would that just waste energy operating another unit?

Last night it didn’t go below freezing, and I just turned it off. (We like to sleep cool). I figured why use electricity running the system when it’s hardly needed. Does the system use significant electricity when not actively heating? Also, I hate that the minimum thermostat setting is 60F (15.5C), which with this system often means above 60F. Downstairs I would turn the setting to lower at night, or when I’m away, if I could.

 KUMXA301A (30kBtu)  LG Multi F Multi-Zone Inverter Condenser with advanced inverter technology.

Wall units. Two of: - KNUAB091A (9kBtu)

Two of: - KNMAB071A (7 kBtu)