Kenny the Pirate has each day's schedule on his crowd calendars for each month (actually, he posts calendars for each week).
http://www.kennythepirate.com/crowd-calendars/ Personally, I don't like his format and it's easy to overlook the times on there...you just have to look under Hollywood Studios' schedule and the time(s) for Characterpalooza are listed there.
The location has changed quite a bit over time. We've done them in the Animation Building, in the Streets of America, and at the Tower of Terror exit, which is its current location. Look for the large gate right past the coffee stand. When Characterpalooza starts, they'll open the gates and the characters will be standing there. The characters that meet rotate, but since they're characters from Fantasmic, only characters that appear in Fantasmic meet at Characterpalooza.
Off the top of my head, over the years we've either met or seen Belle (blue dress), Mulan, Pocahontas & Meeko, Aladdin, Jasmine, Chip & Dale, Captain Hook & Smee, Genie, Goofy, Minnie & Pluto, the Evil Queen, Mary Poppins & Bert, Pinocchio, Gepetto, and Green Army Men during Characterpalooza. There are probably others, but those are ones I remember. The awesome part of Characterpalooza is that it gives you the opportunity to meet characters you can't meet regularly any place else. The not-so-awesome part is that you have no idea who is going to be standing there when the gates open. It's totally worth doing and it's a must-do for us every trip.