I think:
1: Cabin pressure would not change as the air/ground logic system keeps the outflow valves fully open
2: Can't remember
3: Relieve excess pressure
4: Outflow valves must be closed to prevent shipping water - I think there is a specific selection on the A/C panel called 'ditching' -??
5: The mixer mixes the cold and hot air available in the A/C system. Bypass valves regulate the amount of hot air allowed to bypass the A/C without being cooled.
Hope that helps...