Ceiling valves in style - does such a thing exist?

And the others like Luna are stupid for exhaust air? Both have supply and exhaust air indicated...

There is a Luna for draft air and a version for exhaust air, so everything is possible.
Do you have a fireplace/stove heater?
Then I would include an activated carbon filter right away.

Yes, the neighbor is planning something like that, even though I talked him out of it. Is activated carbon extra? So not the normal filter mat?

Correct, you need to clarify whether Vallox has something like that.

For the external connections, you should make sure that the distance between them is maintained.
And remember to have enough valves with the appropriate supplies planned in the rooms.
2 valves are quieter than one :-).