And welcome again, Laura! Nothing wrong with starting out in coach, many of us took long trips on Amtrak in coach before we became old grumps that need a room.
I second all the advice listed above, especially the seating arrangements. I'm not sure how crowded the coaches are this early in the season. Many people get on and off at various stations, so you never know when you'll need to share a seat or not. Trains pull into busy stations in the middle of the night, so you may have someone join you at 2am. People with single seats will pile their stuff on the empty seat, get scolded for it, then do it again anyway.
There are two kinds of employees on trains. The conductor and assistant conductors are responsible for tickets and safety, but they only work 8 or so hours and then change. There is supposed to be a car attendant for each car, who has less authority but will help place people into single seats as needed. They ride the entire length of the train run. Think of it like pilots and flight attendants, except that the pilots walk through the train often and keep an eye on things. If you don't see a car attendant right away, they might be servicing more than one car, or might be on break, or running an errand for someone.
I'm a CPAP user myself, and you might want to talk to your car attendant when you board to make sure you have convenient access to a plug. It also might be a good thing to put on the seat next to you to discourage sharing, but if they need the seat they will ask you to put it in the seat pocket ahead of you, again possibly in the middle of the night.
The food in the cafe car isn't terrible, but it is pretty fast-foodish. If you're lucky they will have some decent cheese trays or cold or hot sandwiches that are a bit better than the microwave burgers. You might want to try and get a breakfast or lunch reservation for the dining car, just to see what it is like. Worth it for a nice change from the cafe. There is a fixed price for each meal in the diner, breakfast and lunch are pretty affordable, dinner isn't. Dining car reservations for coach are limited, so ask when you get on. There is no problem at all with bringing your own food, many people do. Just don't bring anything with a really strong odor!
The scenery is the reason for being there, so make use of the sightseer lounge. It should be available 24 hours. It is also a good way to get away from a seatmate for a while. Both trains are very likely to have the SSL, but there have been a few reports of trains leaving without one because of a mechanical issue. Hopefully that won't happen.
Now that we know you're in coach, let us know if you have any other questions, and feel free to ask any time, even when you are on the train. The trains don't have wifi, but you can usually get cell reception and hotspot to your phone. There will be many places in the mountains where you won't get a cell signal, so if you need to get messages in or out, do it while you are going through a town or along a busy road.
Enjoy!