Bent, at the moment I can still not see myself switch to mirrorless. I tried liking a few of the mirrorless cameras offered, but it just did not work.
I wouldn't mind the 90 degree rotation to mount the lens, because I never expect to swap to this setup very spontaniously. Most of my spider photography and the product photography I want to try next is very scheduled and planned. Setting up the lights takes a fair amount of time, and with that, a little extra effort to mount the bellows will not be a real downside. I am just glad if I find out that the bellows does mount directly to the D800 with this trick.
Either way, the advise I got from you and others, and the sample images did a lot to help me find an entry in this field of photography, and now I can hardly wait to get started, and already have various ideas on how to take this a step further.
But first, I expect a bit of a learning curve.
I did use a Cambo large format camera in the past and loved the experience, so I guess that the first barriers I will walk into will not be related to the multitude of adjustments possible, but rather to limited image circles of the lenses I own at the moment