Having read the SDK I still have difficulty understanding exactly what is the distinction between the various datafiles.

Aircraft.cfg - text file with a lot of parameters about geometry etc.
*.air - binary file
model/*.mdl - visual model
gauges - gauge logic

1) If the .air file is a binary compilation of the flight dynamics - what are all the parameters in the aircraft.cfg then used for?
2) Where do programmers (A2A, Aerosoft etc.) place the more complex system logic, hereunder aircraft specific variables - In one specific gauge?
3) Is there any logic in the .mdl file?
4) Is there any good tutorial to creating your first plane?

If anybody would be willing to ping-pong on the occational newbee question regarding the aircraft It would be greatly appreciated.

Thanks in advance.