Yes, the roles are reversed. If you are attacking the territory with transports, you are also attacking the sea zone around it if there is a scramble. If you don’t put forces into the sea zone with an attack value to deal with a scramble, then the scrambling defender gets to roll defense and after you take any hits you get a chance to retreat.
Furthermore, the land battle still goes ahead but without the forces that were landing amphibiously. The US aircraft in your example still take AA shots from the AA gun, then fire their offense if they survive, then have to deal with shots from defenders, and then (and ONLY then) can they retreat.
The airbase doesn’t make the sea zone hostile. The scrambling aircraft do. This forces you to resolve the adjacent naval combat before you can resolve the amphibious assault.
In response to your 1a, the carrier is “attackless” (it has an attack rating of zero) and therefore does not roll any dice during its attack. It can be hit by the scrambling aircraft, which are defending the sea zone. In that scenario if you take a hit on the carrier, the planes attacking the Carolines dies unless there is another landing zone available (assuming they survive the land battle).
Marsh