If the park opens at 8 (which it normally does on weekends and during busy periods) then the turnstiles don't open 30 minutes prior to park opening, it just opens at 8.
Except at parade times, Town Square is a great place to find characters. Make sure to look on both the City Hall side and the Opera House side. I've seen most of the clasic characters there (Mickey, Minnie, Goofy, Pluto, Chip & Dale, plus princesses, Genie, Peter Pan, Wendy, Captain Hook, etc). Woody and Jessie are often in front of the Golden Horseshoe in Frontierland. I've often seen Belle near the Carnation Plaza Gardens. Near It's a Small World is another good area.