I know the lines for jack and sally are usually crazy. I believe they usually start at 5 though. From what Inunderstand you can usually guarantee a two hour wait for them. We dont do meet and greets when we go. I am totally addicted to the oarade and fireworks and we have gone last year and this year. Last year we went on actual halloween and it was great!! I didnt think the crowds were out of control at all. This year we went on aug 29th and it was CRAZY crowded. I was really surprised. I figured florida kids were back in school and it was a tuesday so it wouldnt be bad. I was soooo wrong. We still had a blast and could pretty much walk on to any ride we wanted though, especially the later it got.
Dont forget you CAN schedule FPs from 4-6 on party days if you plan to get in as soon as you are allowed.
Also dont try to leave right after the fireworks unless you want to be waiting in transportation lines for an hour and a half. Just hang out at the park. We left right before the 2nd parade and got a bus back to the resort immediately. Last year though we left right after the fireworks because DD just couldnt hang anymore, and boy did we regret it.