yeah last year i think the attendance record was like 10-13K for all three days.
As far as looking for other Air Gear cosplayers, I'd make either change the title of this thread to say "Air Gear Cosplayers?" or something to that effect. Also the Sakuracon forum has a good amount of people on it.
It's webname is scmb.sakuracon.org
Good luck, Agito