Amphibious Assault ques.

No.  Land and sea units may not move after being involved in combat (except to retreat, of course).  Only air units may do that.

Yup.  One territory attacked equals one battle.

If a battle occurs before the assault then yes they may, but their cargo goes down with them…

I believe the Play-By-E-Mail system on aaeuropemc.com also uses the 2-or-less rule.
Note that Battleships still offer support fire at 4-or-less in Amphib Assaults.

destroyers only have an attack role of 2 during amphibious assaults.

i’m pretty sure you need a transport to move between islands
the 12 ipc’s is 1 time only, it can be saved and used later, but you don’t get 12 more ipc’s

I know you can buy AAs, but, can you put them where ever you want?

transports have absolutely no value in the combat phase of a land battle. The may not attack, they may not be hit, and they may not be attacked.
The only exception to this is if they are dropping off troops in an occupied seazone in which case they may take hits (killing the troops).