I to design & build and had a mobile office although it wasn't a Benz. As you have already bought the Benz it's a little late for
me to recommend not doing the mobile office. That said, I think you will tire of it so, I would design your interior so it has other
uses than an office. I would agree, no need for a 55" monitor in such a cozy setting. My clients are all professionals, doctors,
etc. and ever since I have been providing them with Chief ray traces, they have all been sufficiently impressed using just a
1920x1080 display. I use a 4k display along with the one just mentioned and I prefer 3D modeling on the 1920x1080. I have
found that Chief is much more interested in processor power than expensive graphics so, I also agree,go with the desktop.
I am curious if you plan to get a generator? One of the things I enjoyed most was setting up onsite to do my initial design work
prior to having power to plug into.
Also, I just bought a Lenovo Yoga Pro 3 and that runs Chief just fine and provides great "on the go"
tech-ness with clients. Anyway, good luck, I think you owe everyone a pic when you get it done.