First of all, welcome Scuby !
It is difficult to say what to build first, but I guess time is your best advisor.
Take your time to work out several options on paper or in your head.
You already seem to have some ideas, and it looks like a "desktop cockpit".
Some chaps on this forum are doing just that!
As soon as you go further than MFD (screens), you will need to connect switches and lamps.
(Side note: If you use Thrustmaster MFD's, those switches are connected via USB).
At that moment you have to decide which "connection system" you choose. Some are no longer
on the market, but you may be able to buy their stuff second hand (for example Beta Innovations).
In my opinion not the best future-proof option.
Check out white-eagle AIC, JShepperd's system, and if you are able to solder and build electronics
the PHCC system. PHCC is not the easiest system because there is no software for it, BUT Ghost
is working on that.
Reading this forum gives you a wealth of information, should keep you busy for days
May the
force wisdom be with you in all skies
- henkie