What maintenance do they actually need? Tires, brakes, wiper blades, air filter, washer fluid? All fairly trivial to DIY. One thing that I would do is disable the cellular modem, to prevent unwanted "upgrades."
> One thing that I would do is disable the cellular modem
Is that even possible in modern EVs? Without breaking critical functions like maps, etc.
You forgot suspensions.
Brakes! They sometimes rust on Teslas due to lack of use.