Completion of insurance, the ideal time during new construction?

Apparently really very confusing.

We bought the complete package from a sales company (=broker). In other words, house with land. However, the whole thing is tied to the completion of the financing.

We signed a reservation agreement for the said plot of land and the end-terraced house in the amount of x €.

So it doesn’t seem to be the "usual way" when buying a house?!?

The company with which we have the construction contract is currently building several dozen houses in terraced housing developments.

Who is the property seller and what is the relationship between the property seller, house builder, and broker?

The property owner is "Immotec Grundstücksgesellschaft mbH" based in Hamburg. The house builder is a construction company located in Schorfheide (on the outskirts of Berlin). The realtor and the construction company work together.

So you have a total of 3 contracts?
-Broker contract
-Purchase contract for [Grundstück]
-Contract for work [Hausbau]

Is that correct? Then it is not a property developer.

So, we have signed
- a construction contract with the descriptions of construction services and the desired additional services together with the supplementary agreement that the construction contract will become invalid if the required financial resources are not approved and
- a broker and reservation agreement for the property

Unusual?
Actually, I just want to know whether the initially mentioned homeowner's and landowner's liability insurance must be taken out

Well, you have signed a house construction contract without having a guarantee for a plot of land. But to your question: Yes, such liability insurance makes sense upon transfer of ownership, but it is not a compulsory insurance.