I personally find AAA provides the kind of psychological threat, making the opponent think twice before flying a bunches of fighters and bombers in a battle, as sometimes losing a fighter and 2 in the long run becomes critical, particularly for Axis.
And so the initial AAA is very important as you might not buy another one for a while.
It’s helpful to have the rulebook handy to reference when questions pop up. Even if you think you know the rule it’s better just to find it in the rulebook and show your friend so that you build trust. After a couple times of being right he will just take your word without question.
Yes, twice the IPC value is correct. The other sentence is trying to say although an IC can’t be destroyed, it can be rendered useless by taking as many hits or more as the IPC value or the territory.