Assessment of the buildability of a large plot according to §34

Preliminary building inquiry procedures during a pending purchase decision are naturally a bit of an issue. I always see the development plan vs. §34 as double-edged: one can be more restrictive, while the other is vaguer (and with narrow-minded blockheads means that every house has to look like a clone of the mayor's house, only the bocce court and garden gnomes can be left out).

The only way to really receive a legally binding statement is solely through the option of a building inquiry, as already mentioned. Whether all your ideas (type of building, height, fence, etc.) can actually be realized will then become apparent.
You basically have only two options: either you buy the plot now and may have to accept one or another compromise if you cannot realize all your wishes, or you "negotiate" with the real estate agent/seller that you still want to submit a building inquiry first and only then buy. However, it is uncertain whether the seller will agree to this.
You have to decide what the plot with its location is worth to you, and whether you are willing to swallow one or another toad or not. Really reliable, none of us here can say how you are allowed to build and whether you are allowed to build your fence that high, etc.

Time does not exist. Verbally check with the building authority again. Tell them how it is. I can buy, want to buy, want to build, will not cheat, there shall be no high-rise, but xyz....I know, you cannot tell me anything legally binding now, but I ask you, give me courage or tell me: stay away. it won't happen. Every official will now speak an honest word. At least every decent human official. And those are the majority. The rest is simply good faith....

because he ultimately did not get his multi-family house project approved by the building authority

If you can get hold of the rejection reasoning, you might already be able to read something from it. A predecessor building is also somewhat of an orientation: would you, assuming, accept an extension of the "foundations" to the desired building height at this place on the property, or does it become significantly more attractive to you the more the new building is positioned differently from the existing one?

Personally, I would very benevolently examine what can be carried over from the existing building, especially if it has a basement.

An extension of the existing structure does not seem economical to me after initial discussions. We also want it to be absolutely individual and not adhere to the specifications of the old building.

But of course, I can also inquire elsewhere again. Maybe a general contractor [GÜ] is not the right choice for the project but a creative architect has to take over? Construction can be done by a [GU].

I like some houses by the architectural firm kirsch-architekten. They are from Cologne. Just Google them; linking is not allowed here. I could get along with the style.

I like Kirsch, Kirsch II, and Heeger. Schmidt as well, only that there probably isn’t enough floor area on the top there..... The problem with Heeger will be that it is too much space for our project. But the style is super great!

It is always advantageous to have an architect who has a good relationship with the respective building authority and to clarify such matters in advance.