BornAcorn: will this do you? Obviously need to fix the fences, and create the diagonal taxiways that are not right, but its pretty much what you had in your picture.
This has 9 terminals for aircraft, 4 helipads, and a darn great big hole!! (7x3), which in my screenie I have filled with bus stations and mail depots.
(I had to write a tiny extra bit of code to handle "holes" in airports. It has a bug - when you come to delete the airport, then all the "hole" tiles are deleted, and can leave 1/2 a tunnel, etc. Its what debugging is for

)
If the station tile inside the hole touches the airport, it is part of the airport (and is detected as such - see screenie). If it doesnt touch the airport (ie. in the middle), its a separate station... woohoo.. nested stations!! Also, you cannot place the airport over existing items... it must be empty space. But you can then fill it with whatever you want.
Obviously no movement states or position data sorted out. This will be *very* hard to code within the 32 states available. The Intercontinental was really pushing it. This will too.