Bonsai is supposed to be left outside and is by definition in a pot, so whatever works as Bonsai should work for you.

That's pretty much right. Any hardy evergreen can, and should, be left outside in the winter. Any deciduous tree or shrub, too. They'll die if they don't go through winter dormancy. The only trees that need to go inside for the winter are tropicals.

But, being in a pot, don't forget to water it, and give it some protection from extreme cold and drying winds. An unheated garage is usually a good place to keep them, or a cold frame. Offer some protection from critters that like their bark, like mice.

If you can't put them in a protected area, pile mulch, or some kind of insulating material, around the pot to help regulate the temperature. It's okay for the roots to freeze, but constant thawing/freezing cycles may destroy them.

And again, don't forget to water them until the soil is frozen. It's easy to forget, I know. I've been told that more trees die from lack of water in winter than from freezing temps.

Good luck, and have fun.