1. No. No unit can be inviolved in mor ethan 1 combat in a single turn.
2. Correct. AF are prohibited form landing in newly captured territory. Any land units that participated in the battle MUST remain in the territory. Other land units that did NOT engage in combat that turn CAN be moved into the newly captured territory in non-combat movement.
3. Yes, land units can cross the canals w/o transports
4. The phrasing was clarified in later editions of hte rules. The “adjacent sea zone” means you can’t offload from a SZ that is hostile… you have to win the battle in the SZ before you can offload troops.
5. The BB cannot be hit by defender fire. The BB fires only ONCE at the start of the first round of combat. The BB can hit ANY unit in the land territory, but the defender chooses what is hit.
6. Aircraft are engaging in combat movement on the way TO battle, and of course they are engaged in combat over the territory they are attacking. Thus on the way in, and for the battle itself, they CAN be hit by AA fire. But after the battle, they “hover” until all combat is resolved, then in the non-combat phase of movement they fly to their landing area, and for that part of movement the AA guns do NOT fire since there is no combat in the non-combat phase of the move.
You may want to switch to using the Larry Harris Tournament Rules instead of the Operations Manual that comes with the game. Many of the things that are unclear (or just plain wrong) in the OM are corrected in LHTR. You can find tha trule-set here
http://www.dicey.net/revised/viewtopic.php?t=92