To meet the celebrities, you will have to get there early. Last year they did 2 signing sessions each day with 60 people per celebrity per session. That means first 120 people in line for each person will get the autographs. Depending on how long that takes, standbys are also given bands. They are not garunteed anything. You can get bands for both if you are at the front of the line. Some celebrities are more popular than others, so they may be easier to get an autograph from. Last year they would only autograph the provided pictures and nothing else. I understand that this depends on the actor but you may not want to carry something extremely valuable in hopes of getting an autograph.
For the characters, normal lines just like any other Disney character will apply. They were out for most of the day in shifts so that there was always someone out but they were not out in the sun for too long. There were cool backdrops set up last year so that you not only got a character but a nice scene behind you as well.
There was no C3PO walking around last year, but there were R2D2 And C3PO statues that you could take pictures with. The only time he was in a parage was when he was being carried by Chewbacca.
The WWTBAM star wars editions were extremely cool, which the characters and some actors and all Star Wars trivia
