I'm also relatively new to touring and have only been seriously cycling for a couple of years, doing mostly centuries and other single-day rides. In all honesty, your plan sounds extremely ambitious for a new touring rider. The distances alone are daunting, but if I understood correctly, you are planning on crossing the Northern Tier in January with little experience and relatively untested equipment. I live in the middle of the Northern Tier and the weather and road conditions up here can be extremely variable. I ride year-round but there are quite a few days in the winter that I don't venture out. In January we can have anything from 20F and sunny (beautiful for a winter ride if the roads are good) to -40F with a howling blizzard, sometimes in the same weekend. Roads can be perfectly clear and dry or they can be black ice edged with deep frozen ruts, or covered with six inches of snow with drifts several feet high that are impassable until the snow plows go through. There are lots of places where it is 20-30 miles between any kind of town or even several miles to an occupied house. The amount of clothing, gear, and food you will need to safely traverse MT, ND and MN during the winter, even in good weather, will be extensive and cumbersome. I'm not saying it can't be done, but you better know what you are doing.
I would really suggest that you do a couple of overnight or weekend tours with all of your equipment, under the conditions you are considering, before trying something of this magnitude.
Good Luck to you, whatever you decide.