90 is a great drive! Very scenic and once you get past the twin cities there's very little traffic. Course you are probably already there by now but for others this can be a challenging time of year crossing 90. Yes, make sure you have chains and even a bag or two of snow melt. Make sure to have a good winter emergency kit and carry all life sustaining supplies. Its always good to have a couple gallons of drinking water and some non-perishable foods. Of course warm clothes and blankets, candles, matches etc...
Plan your trip out carefully. It can be a few miles in between truck stops. Make sure you aren't running on less than half a tank of fuel at all times if your company permits. This time of year if the weather is bad and the highway gets shutdown you may end up sitting for awhile so you want to make sure to have plenty of fuel. Maybe also do a little more thorough of a pretrip and give everything a little extra attention. If you are running reefer keep a little bottle of anti-gel with you. Basically you just want to make sure that you are prepared and your winter checklist is complete. This should be done anyway but running all the way across 90 in the winter should certainly be given extra attention.
As far as the driving and terrain goes, its pretty much flat ground until you get about midway through Montana. Wind can be a factor up on 90 and with this comes blowing snow and white outs. Once you get toward western Montana prepare for the scenery and roads to change. There are some very steep grades out that way! Use extra caution at night and take it slow if you have never been out there. They do have rock slides and even avalanches out there, Snowqualmie is known for this! Not trying to scare anyone but its just something to keep in the back of your mind.
Good luck to all that get to run that route. Its a beautiful run and is one of the things I love about trucking! (in the summertime its a great run to have your fishing pole and a little bbq with you!)