Good layout, and based on five years with two screens, I’ll offer some opinions different from what others have posted…
* Put a 10” screen on the right side, and use it in split screen mode. The half towards the center of the cockpit is very readable says I, based on experience. Only when you go to full screen does it become less readable because the useful information (in the center of the screen) moves farther away. I use the other half of the screen for flight instruments for the other pilot. And being a CFI, flying flight instruments that far away (in case of screen failure) is not a big deal;
* Go with a GTN650. Why? Because on an ILS, it will automatically switch from GPS to ILS just outside the FAF. Much handier than doing it manually. Also, the larger screen will be useful in flight plan editing;
* Disagree with putting all switches in the center stack. The only switches I use in flight seem to be fuel pump and flaps, and the standard location for flaps is to the right of the power knobs;
* Group your switches so that they’re easier to find. In other words, put spaces in between the groups;
* Here’s an interesting concept: on my plane, for various historical reasons, the three power knobs, carb heat and fuel pump are all in the center stack. Makes it real easy to make sure all the engine controls get manipulated at the same time. Handy, yes, which is good. But on the other hand, non-standard is bad;
* You really don’t need master warn and caution lights as the G3X will do those for you. And in practice, the master caution and master warn invoke identical actions, so the distinction between the two is moot;
* I’m not a fan of headphone jacks on the panel as you end up with cords all over the place;
* If the G3X goes dark, oil pressure will be the least of your worries. No need for a backup. For practice, I have flown the plane with no engine instruments on my side (the safety pilot had them) and it’s annoying to fly on knob position and sounds alone, but not that big a deal.
Be well!
Ed