Hi Andrew
That device link software looks good, and those soft gauges look fantastic-- ( there are Me109 gauges as well as the Spit now available) all you would need to build is a face panel to go in front of your monitor and have the cutouts so they match the layout of the plane you are flying.
(curse CFS3 for not being able to extract data)

I think you can even save the position changes of the gauges. This would mean you could have different gauge/positon combinations for different aircraft.
You could design a system of removable face panels that you would slide into their holders in front of the instrument monitor. This would give more flexibility for your simpit and would look great.
Anyhow lets get onto the subject of your interface for all the switches and levers.
Are you going to buy a USB type control unit or are you going to try and do this with a hacked keyboard only and just use old stripped down joysticks for the analog control(ie prop pitch etc)?
I originally had a stripped down joystick that I used for the throttle quadrant. This worked fine.(cfs2 can have 16 joysticks -don't know about IL2 )
All of my switches,levers (gear & trim panels) all worked into a hacked keyboard.
Now the main problem (curse) of hacked keyboards are that you can only use momentary switches.