Greetings @T.Albers - and fantastic to see more of your work. The only thing I am going to try to add at this stage concerns 3D printing.
As noted further up this thread, in recent years I have used 3D printed "quarter scale" items in my passenger car interiors. Some are very fine examples of the miniaturists' art; some, particularly if very small, are as rough as older white metal cast parts. I don't have a 3D printer and have always considered the learning curve too steep or at any rate too long. Based on your experience maybe that's not right - but for the time being I have found an alternative.
Recently I laid in a stock of 3D printed "quarter scale"or 1/48 parts sourced from makers other than Shapeways and have found that the printing of these very small scale parts seems to have moved on a long way just in a couple of years. They must be using a different filament now because the detail and finish are, in a word, staggering in their precision and realism. These are not train car interior parts but they do for my purposes.
You mention a passenger car magazine table with an illuminated lamp. I wanted to put a small table lamp in one compartment of my Lionel 21"/scale "Lone Star" business car. I sourced it from a company called "Tru2Scale" who make diorama and dollhouse fittings.
When I came to the point of trying to put an LED inside it, I found that it had already been molded with the hole for the wire right through the minuscule lampshade support as well as the base. There is such a thing as a Z size LED (available from Evan Designs) that can be threaded up through the lamp and shade - or a larger size can be threaded from the top down if there isn't a resistor installed already.
This is a project in progress and I do not have many photos so far, but this one on the left shows the lamp in place and the second shot shows a bathroom with scale fittings 3D printed from yet another supplier called "LaserShrinkRay" (a British lady). These are tiny enough to challenge a macro lens so not everything is in focus, but note the 3Detail of handles. Most of these parts available pre-painted too, which saves effort and reduces the potential for mistakes - at least in my case.
Bear in mind also that I only produce facsimile/fantasy passenger car interior schemes. With this one I tried to stay close to the prototype, which I have seen, but in the end the advantage of using someone else's machine-made parts won out:
