Got fastpasses for the 11:15 show around 4:30pm on Friday. The line to get them had about 20-30 people in it. Took a few minutes. If you can't take a chance on the addition of a late show, just buy the lunches. I happened to be there around 9:20am on Friday and the line to get into DCA stretched halfway across the plaza. (I honestly don't remember if people were going in yet. I was waiting for friends who were running late.) It was insane. And that was after the 20-minute wait to get on the tram. Probably would have had to show up an hour or more earlier to be anywhere near the front of that line. Sooo not worth it.
Just showed that my "never before noon unless meeting out-of-town friends" rule is valid.
So, in a nutshell, if you must see the show and can't fail, the lunches are your simplest guaranteed ticket. If you can take it or leave it, keep an ear out for the announcement of the addition of a late show then head over to the fastpass distribution. If you've got more time than money and can't fail, show up way early and get a fastpass.
4: Where you go depends on which section you're in. It's printed on the ticket. (The fastpasses, anyway. I assume the meal tickets are similar.) You can always ask a cast member if you're unsure.
5: You queue in holding areas based on color/section and are herded from those holding areas to your assigned viewing area just before the show. Standing space is first-come, first-served. The earlier you get there, the better your chance of securing a spot near the front of your section. There's also the option to stand on the boardwalk and get wet (more like slightly damp unless the wind blows the water right on you). There was lots of room up there at the late show.
6: It's the same show. Procedures should be the same for each showing.