I highly recommend starting here: http://www.mudpond.us/

There are no short cuts with flight dynamics; it's trial and error until you know what the important settings do. I wouldn't start building an air file from new, I'd choose an existing file similar to what you want to end up with, and then modify it. Microsoft used 'airframe numbers' to determine an air file's characteristics, which is why you'd need a similar type to yours. Otherwise you might use a Cessna airframe type when you are trying to design an Airbus A340!

Make broad brush changes in the air file, then do the fine tuning in the .cfg file. There are some things (like braking strength, for example) that aren't modified in the .cfg file, so you have to do it in the .air file. If you are entering actual plane dimensions and other specs into the FD, then you might well need to use the 'flight tuning' section of the .cfg file to get it to fly OK. Then you can modify for engine power, range etc.

Great fun!

Niiccee...  VERY nice....