7) It's the Snecma CFM56-5C4 (I think) 34,000 lb's of thrust.
14) Don't quote me, but I seem to recall something I've read about the 400 pressurising partially on the ground to...a, Seal the doors, b, prevent cabin pressure bumps in the event of an early return after takeoff and c, to provide extra fuselage ridgidity.
18) No worries
Cheers
TTD