Welcome
The closest motel is the Comfort Inn, Gunston Corner. It's about 1/4 mile away. You could walk it, but I don't advise that because of traffic and poor sidewalks. It's a decent, clean place with prices as reasonable as you're likely to find nearby for comparable accommodations.
When you enter the Auto Train station driveway, just go past any cars that are in line for check-in, and park in the short-term parking lot directly across from the drop-off canopy in front of the station. As you enter, be alert for autos being moved around the drop-off area. Don't drive all the way to the back of the property. That's the maintenance area where employees park.
The atmosphere is pretty casual, but it might be a good idea to have your tickets & reservations with you to show in case anybody asks you why you're there. You'll have free access to the station, and probably to the platform, so you should be able to observe the drop-off procedure, auto loading, and check-in at the ticket counter. That's where your ticket is actually taken, meal coupons issued, etc. on the actual day of departure. You won't be permitted to board the train if you're not traveling that day unless you are escorted by one of the ticket agents. Depending on how busy they are, it's hard to say whether they can break away to do this.
Here's a rough schedule of events:
9:30 or earlier --- inbound train arrives.
20 min. later --- unloading of autos begins.
60 to 90 min. later --- all unloading completed.
11:00 or 11:30 --- begin accepting autos for loading (can vary)
2:00 --- Motorcycles & oversized vehicles must be checked in by this time.
2:30 --- begin boarding (can vary)
3:00 --- final boarding call. ALL DEPARTING PASSENGER MUST BOARD NOW. No more vehicles accepted.
3:15 --- begin assembling train. Adding auto carriers, etc.
3:45 to 4:00 --- departure (Schedule says 4:00, but can be earlier if OK'd by dispatcher)
Have a great trip!
Tom
Edit: P.S. The whole station is your "observation area".