Add maybe 1 or 2 more variations to it.
One that resembles a Chinook, with seats on the back and small “doorways” behind the driver and passanger seats.
Another with storage boxes, but no or limited extra sits behind the driver.
I don’t think they should be modular as cars are, just variations you can buy at Air Wolf vendor.
It should be
Tier 1 - Minicopter
Tier 2 - Scrap heli
Tier 3 - Military heli?