Needing to shut off water in an empty building in Northern Montana to save propane heat expense... at times 30 below zero... do I need to do anything with the water main bringing the water into the building? (I plan on draining and blowing out all water pipes, adding antifreeze to toilets and traps.)Will the city need to get involved?

You should have the city turn off the water at the street just to be safe.

Ditto but I would also make sure the traps and toilet are 50/50 Antifreeze

)Will the city need to get involved? No! Simply turn the water off at the meter and drain the line.
Blowing out the water lines and replacing the traps with cooking oil or anti-freeze is necessary,( don't forget the floor drains) and adding antifreeze to the toilet bowl just isn't enough, You have to mix of a bucket of half and half anti-freeze and flush the toilet with it. There's a hidden trap in the bowl that needs to be winterized. Good luck and if you're going on vacation come on down to Florida, Tom