Loved my time with Vader. He came to the doorway, pointed at me then at the spot I was supposed to go to. I just stood there and stared him down. He then said "I sense that you sympathize with the Rebels, how unfortunate for you".
We bantered back and forth with me telling him that I will never bow to the dark side and I tried to remind him that he was good once. Ultimately I agreed to a photo, but told him that did not mean that I take orders from him. The photographer caught some great shots with us staring each other down. Even the CM that had my own camera got some good ones.
The meet and greet is in the Launch Bay. When you enter, head right, then just after Rey's speeder is a little podium where you check in. If you get to the Cantina, you've gone too far. This special Chase Meet and Greet is only for Vader. But for anyone else, there is a line for Vader and a line for Chewbacca. In December, both were averaging 45+ minutes. But the Chase line was only a few people. The longest I saw it was about 10 groups, just before it opened at 4. If you go after say 4:30, there generally is no line.