(A) depends on when you go. During the height of summer vacation season, maybe. When the kids are out of school, families go camping on weekends.
(2) without reservations, do be aware that most campgrounds (and definitely all the ones you might actually want to stay at) see most of their traffic on weekends, so I'd recommend not attempting to move Friday or Saturday nights. Wherever you land Thursday is best kept until Sunday.
(c) Memorial Day weekend, Independence Day week, and Labor Day weekend, plan on both paying through the nose and having a hard time finding anything other than boon docking.