Alan is correct with the typical gratuity for the room attendant. Also in the dining car tips are set based on what you would tip for the meal if you had to pay. Do a rough calculation of your meal cost from the menu and tip accordingly. If service is not good, do not hesitate to not tip. Amtrak service people are paid well, with benefits, so there is no need to reward poor service.

The sightseer lounge car can get pretty crowded, but this time of year it might not be too bad. You have to wait in your room until you get the orientation by the attendant. But after that, you can head back to the lounge (behind the dining car) to check things out. Even if it is crowded, your room with it's double-wide window provides a pretty good view with the benefit of privacy.

The dining car attendant will make the rounds taking reservations. This is another time when it is best to sit tight in the room. However, this time of year the train may not be crowded, so reservations for desirable times may not be a big issue. Sometimes when the passenger load is light they make lunch open seating. If that is the case, they will simply announce the diner is open and you just head back. Breakfast is always open seating.

Boarding at Denver is a little different than most stations. There is a desk set up in the station with separate lines for Sleeper and Coach. The conductor takes your ticket there and issues you a hand-written boarding pass. Then, when the train is ready for boarding, you will be permitted to go down the tunnel and up to the train to find your car and room. The personnel on the platform will assist you.

Hope you enjoy the ride to Reno. It is one of Amtrak's better trips.