I took a train trip about a year ago and have another planned for next fall. In fact, we went to DC, so we were on the very train you'll be riding. I was very satisfied with our train experience, and I'll throw out these details:
-- The earlier you buy your tickets, the cheaper they are. Also, if you're a
AAA member, take advantage of your discount.
-- The cost of those little roomlets is outrageous. You might as well fly.
-- The seats are wider than those on an airplane, and you'll have two electrical outlets for each set of seats, which is very convenient.
-- You can get up and walk about. You can go from car to car.
-- You can walk up to the cafe cart, though I warn you that the food isn't very good and it is expensive! I've heard that the people in the roomlets get better food. Next time I'll bring a little soft-sided cooler with snacks so I can buy just sodas.
-- There's a water-spigot for refilling your water bottles (it's on the wall outside the bathrooms).
-- The bathrooms became progressively more stinky as the trip progressed. As more and more people get on the train, they "open up" more cars to the back . . . so if you pay attention, you can go use a "brand new" restroom. Next time I'm bringing Lysol wipes anyway.
-- I can't say enough good about the conductors. I was with a youth group, and a couple young drunk guys were behaving badly towards some of our young ladies (up in the cafe car). Two of the girls came to get me, and before I could walk up there, the conductors had already taken care of the situation. The head conductor took them up to the cafe clerk and told her that he (the drunk) was to have no more alcohol served to him (he complained loudly, but to no avail), and he (the drunk) would be sitting out the rest of the trip in the little area reserved for the conductors. He did not look pleased to be sitting up there with the staff instead of walking around freely harassing 14-year old girls, but I made a point to thank the conductor for taking care of my girls.
-- The train does stop frequently, so it's not nearly so fast as a plane . . . but you're not doing the driving, so you're going to arrive better rested.
-- You'll have space above your seat (just like on a plane), and it'll easily hold a rolling carry-on suitcase. They also have a limited amount of storage space at the front of each train for larger suitcases -- but you must get those on and off the train yourself, and you might not be able to sit "with your luggage". I suggest packing lightly.