How close to the floor and ceiling should drywall go?
There is no hard and fast rule about drywall to the floor. The walls should be kept tight to the ceiling drywall. That is the ceiling drywall is applied first then the walls applied tight to the ceiling, leaving a gap on the bottom.
In a new house with precut studs at 92 1/4", double top plate and single bottom plate. The ceiling height is 96 3/4". This leaves 1/4" clearance. The baseboard is used to cover this gap up as well as hold flooring edges down.