1. A one-day ticket is good for any day.
2. The first year, it was great. Not very crowded, got to see everything we wanted, lines weren't bad. Last time was the exact opposite. Lines were horrid and closed a few hours before most panels. Just the line to get in took an hour and we already had passes and were in the member line. Completely unorganized. They have tried to reassure that this year will be better. We'll see. I think the main problem last year with the panels was that the rooms were really way too small. We did get into the marquee presentations that were in the arena, but had to make sure we were in line at least an hour before. Things not in the main arena were really hit and miss. I think we waited 2 hours for the Brave panel but got in no problem. There was another one we tried to get in (cant' remember what) but the line was closed 3 hours before it started.
Overall, it's fairly similar to Comic-Con but on a much smaller scale. The floor is divided into different parts:
D23 Dream Store where you can buy all the official licensed merchandise for the event, The
Disney Store had an area, Disney Imagineering had an area with displays of new attractions coming and also a store which there was always a line to get into. There was a small section of the floor for outside venders/exhibits (travel companies, collectors selling rare goodies, authors, etc). There are characters out here and there, service projects to work on, new games you can play. Very similar to Comic-Con.
3. Just like Comic-Con, look at the schedule when it comes out and know what you want to see before you go. If you go to see anything in the arena, count on them taking your camera, cell phone, or any other recording device you might have. They won't do it for everything but they will if you go to the films or games presentation because they will be showing things that aren't released yet and they don't trust you.
My #1 tip!!! If the Disney Legends presentation is the day you are going, GO! It really was awesome, even my husband thought it was special and he was just along for the ride to this one. We saw Jodi Benson(sang), Anika Noni Rose(sang), Lea Salonga(sang), Paige O'Hara, Regis Philbin, Tom Bergeron, Jim Henson's family, and the best ever Disney Moment: Kermit and Rowlf singing the entire Rainbow Connection from a log in a swamp in the middle of the stage. The whole thing was amazing and I cried. Thankfully the did let you take your cameras into this and I have a ton of great videos.
