Reminds me of CoC's set of scripts for OFP that handled respawning of groups. I used that in conjunction with a transport manager script to do something very similar to this as a proof of concept mission.
It actually is fairly simple, but the code will be long to get it right.
I'm still brushing up on new commands so I can help with some suggestions only right now.
First, I want to say your CTI was reall fun to play for Arma!
Second, is it important the AI "capture" the airport in the beginning? From the sounds of it, you almost want the mission to start with it already captured. If it is critical the AI hold the airport to the rest of the mission why make it complex and prone to problems by having them take it by force.
For respawning, you can make it fairly simple. A loop with C-130s flying in is not hard. Every time they land, you can spawn a script for AI/Vehicles to depart and "report in" to some AI manager. You can make it fixed or random units.
For managing where to send AI units, I would suggest game logics or other denotations of "priority" targets. Run a script that repeatedly checks which areas would be best to cover or hold. Have the AI assign units to the area. With some of the new commands, you can assign a whole AI group to a target and have it check the # of remaining units in that group and if it is strong enough, create waypoints for them dynamically.
To make it REALLY dynamic, have the AI manager assess it's force size on a regular basis instead of just acquiring location by location. Maybe the AI falls back to reinforce an already captured location because it is spread out too thin? Also, instead of simply sending them to a location directly, have them sent to secondary game logics which surround a held area which are placed at key points (choke points, etc..).
I could really go on and on about how to improve the AI tactically with methods I have proven to work since OFP/Arma - including the use of FSMs as the "management" part, but the post would be 100+ pages long
I would also LOVE to help code something like this, but alas I am working my butt off just to keep a roof over my head right now.
In a missions with this many scripts going on, I will suggest that you break apart scripts. For example, it might be obvious that you only need to run an AI assessment every few mins. What is not obvious is that if you have it execute the whole assessment in one spurt you will get sudden drops in perf those every few mins. Instead, have it run the count of it's forces first... wait a bit... take those numbers and assess locations... wait a bit... have it assign groups and create waypoints. Rinse and repeat!