Floor plan of a duplex house with approximately 165m² and 150m² / with gable roof / dormers

Why don’t you let your friend do such things? He knows how heights work.
By the way, he also knows how to comply with the floor area ratio and site occupancy index.
Here in BY, you are allowed to build garages up to 9 m in length on the neighbor's boundary.
The converted attic doesn’t work that way. According to your last section, even less so.
How to plan a house is known by the experienced planner/architect. Such things won’t be told to you by the BA.

Oh... things like the fact that the posts aren't really addressed or that the draft is practically set in stone, ... but _such things_ do cause some confusion ...
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yes, it still needs to be optimized. It doesn't look very elegant. The attic hasn't really been the focus so far.
Maybe change the stairs

The standard land value here is 1500/m2. (Sales value per m2 at about (8-10 T/m2) Therefore, a certain standard must also be taken into account in this regard.

Then 3k per m2 is rather unrealistic. Higher standard and BRW 1500 tell a different story. But it's OK if the financing is secured.

Still, I would never design a ground floor with so much dead space. Office with 2 staircases going up?

Architect (friend) is below market prices.

Maybe it would be better to have him design it. Or does he only approve the amateur planning?

Maybe it would be better to have it designed properly. Or is he just approving the amateur planning?

It is now the 3rd revision, so before everything has to be redone again, I wanted to coordinate the important things in advance with the building regulations office. The designs are by me :)

This is now the 3rd change, so before everything has to be redone again, I wanted to coordinate the important things in advance with the building regulations office.
The drafts are from me :)

There is nothing to coordinate. There are regulations that must be followed. If you want to deviate from the development plan, then have your friend submit a building inquiry.

If the drafts were from your friend, I would question that friendship.