Demolition of single-family house, land subdivision, and new construction

Hello dear forum members,

I am currently considering buying a plot of about 1000 sqm including an existing building. The house from 1970 is a prefabricated house and, in my opinion, it is no longer worthwhile to renovate.
Now I am thinking about demolishing the old house and splitting the plot, since I don't need 1000 sqm and the proceeds from the sale will of course benefit the house construction budget.
Now to my questions:
Does anyone have experience with the demolition of prefabricated houses or houses from around 1970? Were many substances used at that time that today must be treated as hazardous waste? What about the costs for a demolition (approximate values)?
The old house has a basement; can the excavation pit created by the demolition possibly be reused for the new building?
Does the demolition and splitting of the plot require a new or additional development if another single-family house is built on the other half of the plot or if one builds a semi-detached house with the new owners?
Does the purchase price I paid for the entire plot including the existing building have to be disclosed to the buyer of the second half of the plot, or is it visible somewhere?

Maybe someone has already completed a similar project and can answer my questions.

I look forward to your replies.

Best regards
Matze

"Allowed" because the floor area ratio and the development plan permit a larger construction or subdivision of the property, or even a duplex?

Yes, a subdivision is allowed according to the municipality and has already been done one property further. Since it is an old district, there is no development plan. Construction must follow the surrounding buildings. In the immediate vicinity, there are already semi-detached houses and single-family homes, which we would use as a reference. I would possibly submit a preliminary building application. But now please back to my questions.

Good, because before I take the time to answer your questions, it should at least be ensured that not only the basic idea is present

1. Yes, a demolition company has experience. They will also provide you with cost estimates. Regarding asbestos, etc., an expert must inspect the house. They should be able to be contacted through the demolition company, if they do not even offer this service themselves.
2. The basement must meet structural requirements -> hire a structural engineer.

Perhaps there are experts near you who can evaluate 1. and 2. together.

3. Of course, when building behind, the lines as well as the access road to the new house must be laid. The whole damn thing has to go somewhere after all. A flat rate length is always included with the utilities..

4. No, why? Payment is made according to market value. For a little gem, you can also get your price.
However, I cannot help you further regarding speculation.

Hello Matze

Removing the old basement, putting in a new basement is a labor-intensive and costly undertaking. Why not take the existing basement, spruce it up a bit and build the new house on it? Would save a lot of money. Even in the 70s, they sometimes did good concrete work.

Steven

old cellar out, new cellar in, is a labor-intensive and costly undertaking. Why not take the existing cellar, spruce it up a bit and build the new house on it? Would save a lot of money. Even in the 70s, concrete work was sometimes well done.

Sprucing up is not enough in most cases; without expert and structural assessment, no provider will build on an existing cellar. Besides, a new building would then have to orient itself to the existing staircase location. That might fit, but it doesn’t have to. Rhineland regards