I'm not sure i understand this: "being able to play this AI aircraft on a mission".
When a condition is true, the trigger should execute START command, and AI will come to life and execute the task, like you said:
"it should be able to make it wait for an order from the player"
For example:
MISSION START >no condition > RADIO ITEM ADD (START My Ai / Flag 1/ Value 1)
ONCE > FLAG EQUALS 1 > AI TASK SET (choose your START command here)
About this issue: "or the detection of an enemy nearby initiate takeoff" - this was present in earlier versions (called GAI task), it was removed, i'm not sure if it will be added again.
To simulate it, add a zone in ME, and set the radius to cover the radar detection zone.
then:
ONCE > part of coallition in zone > AI TASK SET (choose your START command here)
Hope it helps you :)