Indeed, as fender3x suggested I wrote Baicz and got a nice answer!

My Question:
Is there a reason why the bridge shouldn't [...] be mountet with the screws through the whole body and sleeve nuts on the back? This seemed to me a very strong connection?
The Answer:
Hi Moritz yes that would be an incredible installation for sure! I'm confident I would improve the instrument! J Babicz
So... i went for it. Checked suitable sleeve nuts and drills,...
I learned what a Forstnerbohrer is, and looked for suitable sleeve nuts (found some intended to mount railings on boats).

...and finally had the guts to drill. Ok, to have a colleague helping me drilling

Holes for nuts from the back:
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Holes filled with nuts back and front:
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And finally a mounted bridge:
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So I guess I'm now ready for "mock build".

Last remaining woodwork seems to me to predrill the holes for mounting the neck and one hole to establish an earth connection with the bridge.

Thanks to everybody here encouraging me! Most likely the slowest project in this forum...