Good replies so far. Your sleeping car should be either next to or one more car further away from the dining car. Yes, you will have to walk 1-2 cars to get to the dining car.

You get free meals in the dining car, but wine or other alcoholic drinks cost extra. You should tip in cash an appropriate amount based on what you ordered, but the food is free. As stated by other posters, snacks or drinks in the cafe or observation car are not free.

I always bring my own drinks and snacks on an Amtrak trip, since I don't like the Pepsi products they serve on the trains. There is a little bar at the top of the stairs in the sleeping car with coffee, tea bags, small water bottles, and juices. Some car attendants keep a foam cooler with ice nearby, some keep the ice chest in roomette #1, just ask the attendant where to get ice.

Since you state you have a disability, do check your two large bags. When the train pulls in and the personnel get out on the platform, state that you're disabled and might need additional help. I've always found Amtrak people very helpful with any physical infirmity.