Crius,
The car as I have designed and will build it will be functional, I planned to be able to drive my 13lb. tank onto it (I have yet to design and print out the ramp the Germans used).it should be strong enough. I have also designed the axles for ball bearings, so it will roll smoothly. If I planned to use it outdoors as part of a Garden Railway I would print it out in ABS plastic or another type like HIPS.
I removed the coupler from the bogie the actual rail car had the couplers attached to the ends of the chassis not the bogies.
If I were to construct it out of metal (Aluminum) I would get the basic chassis/frame CNCed out of a single plate for strength the sides are separate beams on the real car so I would do them the same way and just bolt them to the chassis. The bogies could be built up from CNCed plates as well the ends are nothing more than "C" channel beams but unless you have the ability to Heliarc small Aluminum pieces I would probably use brass instead
If I were to build the car completely out of brass, the chassis could be built up from brass beams or I beams the same as the prototype, you would still want the bogie sides CNCed as there are many cutouts in them that would be painstaking to do by hand, with a dremel tool or other tools especially to do four that match. The guy that scratch built the one in 1/35th scale had the plans all scaled for his build out of plastic sheet they could be adapted for a CNC to make those same parts out of Aluminum or Brass once scaled.
Plus he did all the work and drew them up in a CAD program which look great, he may not be willing to part with those files as he has put in a lot of time making them.
I will post a picture of what I have printed so far, soon I will be ready for assembly. That is when the fun really begins, still designing some smaller details and lots of sanding before I get to the assembly part, but I am test fitting as I print things out..