1)Does anyone know of a date that has had more than four different World Title changes over the years?
I'm too lazy to check now, but I bet there'd be a lot of changes at the end of March/Beginning of April because of WrestleMania. I'm sure in 17 years the show has happened on the same date a few times.
Well technically, both titles changed hands on December 9th, 2001 when Jericho won them both from the Rock and Stone Cold. But if you're talking about before being unified then yes that is the only time that the WCW and WWF World Titles have changed hands the same day. I didn't check as far back as NWA though.