Just guessing here... but I think I MAY have answered my first question. The CV itself is a ship, fighter hangar, and bomber hangar. It is also a boat entry point, but that is not destroyed when the CV goes down, so I am guessing that is assigned to the task group as a whole, and not just the CV. (if you manually destroy the boat entry in a task group in offline practice, a fire starts just off the side of the CV, which never happens in the arenas)
Anyway... if you add the hardness values of a fighter hangar, bomber hangar, and ship together, you come up with 7.1429... which would require 8 1000 lb bombs to knock out. I am guessing that they have it coded somehow that all 3 of those must be destroyed in order to sink the carrier.