C++ isn't really required for 80-90% of this, but it can obviously be useful, and shouldn't be too difficult if you already know some C++
Admittedly, building FG from source is the most daunting task here. I'd suggest to give the superbuild a try:
http://wiki.flightgear.org/SuperbuildOn Debian/Ubuntu Linux, you can also use this instead:
http://wiki.flightgear.org/Scripted_Com ... ian/UbuntuOverall, it would be a good idea to at least learn some git basics, so that you can easily use fgdata and clone the fgplot repository.
I would strongly recommend to look into fgplot and continue with its development, see the wiki for details.
It isn't the most stable code, but it's a solid basis for anything related plotting 2D graphs.
Note that there are also two sub forums that you will find of particular interest, the Nasal sub forum and the Canvas sub forum.