Hi and welcome to the FlightGear forum!
It depends a lot on what you want to achieve. You can do a lot, lot of things without ever touching the code.
What are you planning to do more specifically? A fixed base simpit with multiple monitors and some hardware as an interface between the control panels and FlightGear? I think the only code you would have to touch trying to do that would be Arduino code in said hardware, though you would still have to do some work configuring the setup through various xml files.
If you have specific data for an aircraft, you will "only" have to model the aircraft and configure it up, including a flight dynamics model, using a few xml files.