As long as you have an ADR, you will get a car. The tables in the back are for walk-ups. If you are concerned, you could mention it when you check-in at the podium, but that is how it was always explained to me. By the way, this is one our all time favs and a must do on every trip.
We've been told the same. Some ADRs do choose the tables.
I think the ambiance is the best Disney has to offer. It immersive theming. But, you do have to think cheesy Sci Fi trailers are fun, not mind the dark, and not mind sitting in those strange cars (they aren't really designed for comfort or chatting).
The food - well, they make milkshakes with alcohol in them, it covers up some sins with the food.