Submit a building inquiry? How does it work?

Hello everyone,
I am new here, so I will briefly introduce myself - I am 42, have a [Früher] and 2 children and would now like to move "to the countryside" from Hamburg.
For various reasons, we want to build a bungalow - but I now have the idea to add 1-2 granny flats to a (large) bungalow.
Now I possibly have a plot of land in sight that can be developed according to §34 Baugesetzbuch.
As far as I understand, I would have to submit a preliminary building inquiry to clarify before purchasing the land whether my project is even approvable - but what do I need for that?
Many greetings from Hamburg,
Thorsten

The section is called "General Questions," but your question is very general and raises many questions itself.
How well do you know planning and construction law?
§34 for sure?
Any other existing local statutes queried?
What exactly should be clarified in the preliminary building request? Only planning law matters, e.g. whether an extension fits into the existing development, or also building regulations, e.g. whether the clearance areas are still sufficient?
Do you need absolute legal certainty, or is a verbal assurance enough for you?
What use is the approval if it doesn't fit structurally?

What use is the approval to you if it doesn't fit structurally?

For me, ...

however, I now have the idea

... doesn't initially sound like it's already been calculated either.

How big is a large bungalow?
Size of possible plot?
Feed us with more data.

Spontaneity and sudden ideas are not good partners in official matters. For me, such things belong in the hands of architects anyway. Apart from that: a bungalow with two apartments on it is not a bungalow, but a three-family house. Who wants to build themselves just to have two tenants stomping around above their head? And then there are 6 cars in the front yard, 4 of them strangers', and you act as the janitor for them, no thank you.