Beautiful trip and my favorite in the country. Just went through a couple weeks ago and there was great snow cover on both days.
most stops are a few minutes but you cannot get off. They have a handful of fresh air/smoke breaks where the train will stop for a bit longer- Glenwood Springs, Grand Junction, Salt Lake, Reno & Sacramento.
Do not leave the area immediately next to the train in these stops. They are to get a quick cigarette, breath of fresh air, stretch your legs etc. in particular at grand Junction the town is very close. People are left behind fairly regularly because they think they can make it to town and back. You will be stuck and on your own to get the rest of the way.
Just before Frasier-Winter Park you will go through the Moffat tunnel which is very long and the conductors will make an announcement to stay in your car and not move about the train so exhaust doesn’t come in. Right after exiting you will get a nice view of the ski slopes when exiting the tunnel on the left side.
Both sides of the train are spectacular. No preference for the first day. On the second day the right side will give you a view of Donner Lake as well as the SF Bay when coming into the Bay Area.
No way to tell which side your room will be on until you get on the train. It is completely random and luck of the draw. You cannot request one either.
Take a look at both sleeping cars at some point. If one has wood paneling along the hallway then it is generally a refurbished sleeper which means the bathrooms are a different design. The toilet is at an angle which gives you a LOT of extra room when using.
Dinner will be by reservation (they will come by in the mid afternoon). Breakfast and lunch are generally first come first serve on this route. Unless the train is late you should be able to get breakfast on the train out of Denver.
In the dining car they will give you a check to sign. You only need to sign the bottom and put your room number and car number (so make a note or bring your ticket to remember it). Don’t fill out the rest with what you want. The dining car staff will come by to take your order and will complete this section. Also meals are included. Alcohol and gratuity are not.
If you want to go to the lounge car (has larger windows) go early. Seats will fill up quickly for the scenic parts. Usually I prefer to sit in my room and have quiet and privacy and view from there, but you can only see one side of the train this way.
I hope you have a fantastic trip. In my opinion this is the most scenic in the country.