Oh my goodness, this is enormously helpful! Thank you so much!
I'm putting some comments in blue below.
Dinner is separate for coach and sleepers. They each have their own dining car so you might want to ask if it's possible to eat together. Most of the pictures GrnMtnMan posted are from Sanford in particular the waiting area and entrance as well as the check in area. Lorton is very similar and the pic of the cars sitting under the canopy are from there. There are scattered outlets throughout the waiting area. the Lorton one is larger. I'm pretty sure you can board first. I haven't paid attention the last couple of trips, but they used to board those in wheelchairs first.