As for yhe overlay material - something like that which was used with the Evolution: UC-33 would be good. It's thin flexible plastic but also durable. They were pre-printed for particular applications though.
Google it and look at the images.
A material thin enough to pass through the card/photo paper slot of an ink-jet printer would be ideal.
That way we could have a template file (MS Word doc, PDF), to which we could colour and label the knobs & switches,