Pretty hard to guesstimate as the celeb lines will not be equal on any given day. Some of the CM's will have the fast passes sorted into sets of the various sessions and you can ask for a certain one. Don't count on getting it, but it doesn't hurt to ask. Some people may be willing to trade times with you as well - you never know.
My guess, given the celebs list, is that the regulars will be there like always - before 5am and a solid number of folks trickle in until 7 - then the general people start to really line up. You'll start to see the Disney transportation users coming around 7.
I don't know how they decide the number of passes per session - it all depends on the specific celebrity and I'm sure - how much they charge per autograph. What we "heard" last year was that Anthony Daniels up'd his charge at the last minute - around $60 per signature and Ashley Eckstein was around $25 per signature. Thus you will see a variety of set ups and enforcements at the sessions. There will be a CM at each tent who has as clicker to count how many times the celeb signs.
On one hand its crazy how serious it gets and on the other hand most people who just go for one weekend and 1 or 2 autographs wouldn't notice any of it.