Marine Atlantic recommended arriving at the dock two hours before departure, and they meant it. Loading the ship is a slow process. Rates differ depending on age and type of vehicle, so consult the ferry service for detailed information. Accommodations are booked solid well in advance, so be sure to reserve early if you want them. The cabins are cramped and very basic, but not too bad.
Good showers are available in the rest rooms.
The ship's cafeteria serves good, plain food at reasonable prices. We had pork chops one night and fish for most other meals, and always lots of french fried potatoes with gravy. The Sir Robert Bond looks like a pretty old boat, but it's been kept up reasonably well and most of the areas have been updated to rougly approximate what you'll find on better Amtrak trains. I think some provisions have been made for handicapped passengers, but it would probably be hard to get around if your mobility is limited. Aside from eating and drinking there's not a whole lot to do on the boat, so bring a book or two and just relax and observe the interesting mix of passengers on the trip.