The default key command for afterburner/reheater is Shift-F4. F4 alone means 100% throttle.
As I said I don’t recommend changing the threshold in aircraft.cfg as it is set to zero for a reason. But feel free to experimment.
Regarding the website you mention: I tried to contact them some time ago but they did not respond even when I threatened them with legal action. I also tried contacting Danny Garnier (the uploader) directly. He is a total moron who thinks he’s doing me a favor and does not understand that his action is a criminal offense in both his country and mine. But this is basically a fact of life as a developer and I just try to ignore it.
If you want to start modeling and/or texturing I suggest you begin by installing the SDK for FSX. After that, a good starting point is fsdeveloper.com where you can find lots of tutorials and documentation.
Good luck! /Tom