Hi
Welcome to Mobiflight !
Like in lots of other topics i must say, that with this thematic DISCORD is the much better place
https://discord.gg/99vHbK7
There we can chat or talk via voice.... Much more easy like here in Forum.
Cause your request is not a single question and also not just a couple of questions...
What you need is personal guidence and something like a initial advisory about the basic thing to push you into the right direction!
If you like.... Join our server and get in contact to me. Then we can talk about all this stuff.
*************
To shortly comment some of your Points.
Q1:
The Design of those Panels is pretty individual. Each Pilot got other prioritys..... There are some Basic Ideas in real, but also these are not fixed in case in Virtual Sim we are not bound to regulations of FAA or ICAO Rules. So we can do what we like to do.
So this question will be awnserd pretty sure in 10 different ways if you ask 10 different Pilots !
I will give you my point of view.... But this NOT must be the right one.
I would see the whole instrument with the 2 Lines as ONE Part. So i would not make a Mode selector for each individual.... I would make ONE Selector and use 3 Modes overall.
Mode 1: Com1 and Nav1 ..... Mode 2 Com2 and Nav2 .... Mode 3 ADF and DME
But at the End..... I would not Build this panel myself.... My Policy is " See Everything at All time" So you have a Individual Display for each Value..... Without there is a risk of Issues.
e.g. if you select a VOR on Nav 2 by fault cause you think its Nav1 and you fly 30 Mins in wrong direction.
Or you talk by fault with wrong atc Center in case you thought you select Com1 but you was in the Mode for Com2.
*****
About Q2:
This make no sense to me.... Why do you want to show current Alt, Speed and Heading ?
You know your Alt from Altimeter, your Speed from Spedmeter and your HEading from the Gyro Gauge.
What you maybe think about is the AP Panel where you see the selected Alt, SPD, HDG and so on for the Autopilot:
But here we need to talk about Input Encoders and Buttons also.
Whatever.... If you like to show these 3 Values.... For sure its possible.... And you can also show ALT as feet or as Flightlevel hardcoded.
As you expect... ALT/100 is the format for Flightlevels.... ( But not realsitic cause in real Alt below Transition Layer are in feet and no longer in Levels)
****
About Q3 a
Question is what you need. E.g. the Master Battery, Master Avionics , PitoHeat, The Magneto Starting Rotary Switch e.g.
Again a question what you expect to do..... If you run the Sim with a Aircraft fully ready on Runway you not need the Starter, cause it still running after load the sim.
So Ask yourself WHAT you like to controll by these switches.... Then think about the needed Number of Switches at the end.
About Q3b
I would not do this.
If your Buttons be able to backlight then its fine. If Not then it make no sense to have a all time lighting LED nearby .... Specialy if you think about Orange and red what can confuse you.
Think maybe about a passive Light somewhere in the edges to fully illuminate the whole Panel. Then you see it at night.
Also in most Sim Aircrafts there is no LED that show Status of e.g. Taxi light..... You will see the taxi light by looking out of the window.
Also LATCHING Switches normaly never have a LED indication.... You know the status in case the switch is e.g. in upper or lower position.
Those Status LED are used normaly for Momentary Buttons. Cause here you need to know if the system is On, Off or Fault.
And here Colors come to play.... Each Aircraft can be different.... But logical is.... RED mostly is a Warning ( E.g. Fault) Green mostly indicate ON and for OFF mostly there is no LED..... means no light means mostly OFF.
And about PRemade Backlight Buttons.... You will not find them.
Backlight label text is build within the Panel plate. E.g. you can buy a premade one or you create it with a CNC/Laser.
There exist some Button styles with a illuminated front.... But also here you will not find a Button with text "Taxi" .... You must again label the Buttons yourself.
I recommend to stop thinking about backlight in your first trys. This is a element you can use when your experience is better in the future !
************
Summary:
All is possible. The question is.... What do you like, and finally will you be happy with some of your unconcentional ideas.
Here the personal guidance is needed i talk at beginning.... Cause you need to think NOW about the LATER usage in the final build.
While the planing process it sounds logical to have a Display for the current ALT.... I will show you that this is not really needed.... and then you can rethink if you say "Hey i still love it" , or if you say OK then Transponder is more usefull instead of show Alt on that Display !
Feel free to call me on our Discord !