Amtrak Watcher,
First class is indeed a separate car and only passengers riding in First Class are allowed into the car. Seating in the car is 2 on one side of the isle 1 seat on the other side of the isle. This provides for nice roomy seats that are larger than the typical seats found on trains. Some seats face forward, while some face backward. There are seats that have tray tables and then there are seats that are adjacent to a real table that you can do work on.
The car is brightly lit and has very large oversized windows, at least by comparison to most train cars. Only a Superliner lounge or a dome has larger window.
Depending on the passenger load you will have either two or three attendants at your beck and call. They will provide you will newspapers, your meal and all drinks. Everything is comped, including the alcohol (as much as you can drink). You pay for nothing while on board, other than tipping the attendant as you leave (assuming that they did a good job). The menu typically includes three dishes, including one vegetarian dish along with a lighter choice in case you’re not too hungry.
Now there are indeed separate lounges, called Club Acela, that are located in Boston, Penn, Philly, and DC. I’m enclosing below, the blurbs that I have saved and use whenever I advise someone traveling in First Class on Amtrak.
As a first class passenger you are entitled to utilize Amtrak's first class Club Acela lounges. These lounges are a nice quiet refuge in the often-bustling train station. They have nice plush chairs, conference rooms, computer terminals, newspapers, TV's, free soft drinks, juices, coffee, tea and clean safe bathrooms. They also allow you to board your train before the rest of the masses.
Should you find yourself in Boston the lounge is actually upstairs above the ticket windows, the door is to the left of the windows and to the right of an information kiosk. There is a small doorbell to the right of the door. Just show your tickets to the attendant at the desk and you're in. They will announce when your train is ready.
The lounge in NY can be found to the far left of the NJ Transit ticket windows as you face them. Walk past the West Gate for tracks 7 & 8 on the left side of the escalator and you will see a sign on the corner of the wall. There is a doorbell to the left of two gold doors. Ring the bell and wait for the click to open the door. Note: In NY there is no pre-boarding ahead of the regular passengers, but they usually do announce your train in the lounge before they announce it in the main station. This means if you don’t dilly-dally, you can generally be near the head of the line at the escalator.
Down in Philly the lounge is again on the second floor, but the entrance is kind of hidden down a long hall in the corner of the station. Walk down towards gate 1 and you should see the hall leading to the stairs. Go up the stairs and ring the bell next to the door.
In DC the Club Acela Lounge is located behind the information kiosk, which is in the center of the waiting areas between gates D & E. There are two large wooden doors there, ring the bell to the right of the door and the attendant will let you in. Show your tickets and you’re in.
Have a great trip and enjoy!