The stacks rule is clearly stated in the middle of page 7 of the rulebook. You can only have 2 aircraft carrier stacks, for example.
I’m not seeing the detailed rule about the Factories and AA guns after a quick look.
@The_Good_Captain can you point us to the clear rule about limited Factories and AA guns if there is one, and expound a little on how the groups must stay together?
Like if you had 3 aircraft carriers in 2 groups, could you move them in 3 different routes during the combat movement phase (say, to establish a retreat route) if you end up in 2 different locations (since you have only 2 plastic carriers)?