Process of construction planning & building - Is a preliminary contract with the construction company necessary?

No signature without a construction service description. Where else would we end up?
Pre-sampling was also offered to me by Streif Haus, Bien-Zenker, and Hanse. It usually depends on the salesperson.

At Streif Haus, we were not offered the opportunity; it actually seems to depend on the salesperson. However, I do not have much more experience with other companies.

At Fingerhaus and Luxhaus we could have done that too. The construction service description came with the offer or was handed over during the initial meeting. Contracts, before which the construction service description was NOT available, are no longer valid by now. Although not a prefabricated house, Viebrockhaus attached the construction service description directly in the catalog and the sample exhibitions are public and have price tags in the model house park. You can simply walk through and see how much you need to budget.

In the end, we decided on a smaller regional company and do the sampling with the individual craftsmen/dealers. At the moment it looks like the garden could turn out much nicer than expected (or we might still do Smart Home after all )

First of all, thank you for your quick and abundant information.

We have already noticed that there are massive differences among prefabricated house companies. The differences mainly concern the building fabric, insulation systems, quality of advice, and services before signing the contract, just to name a few.

As an alternative, the classic construction with local companies and an architect is still an option. Here, of course, the planning uncertainty and the risk of possible botched work in individual trades is felt to be higher.

Would it be possible for someone with experience to name the main steps involved in "classic construction" without a prefabricated house company? Who carries out a cost estimate for the construction project in this case? How much lead time should one ideally allow for the first step? (Construction companies are unfortunately currently incredibly busy)

And one last question. If I pay in advance for an architect’s services or ground investigation, can I still include these costs in the financing of the construction with the bank?

Greetings from the Munich surrounding area

As an alternative, the classic construction through local companies with an architect is of course still an option.

And of course the more or less large general contractor or main contractor who builds brick by brick. "Prefabricated house" is used for houses made of prefabricated components that are only assembled on the construction site (mostly timber frame or timber construction, but there are also stone systems). In the past, our bank recognized paid invoices as equity capital; I would say that is common.

and one last question. If I pay in advance for an architect's service or soil investigation, can I still include these costs in the financing of the construction at the bank?

yes

Would it be possible for someone with experience to tell me the main steps involved in "traditional building" without a prefabricated house company.

in short:
You hire the architect. He first designs a rough idea with you of what the house should look like and estimates what it will approximately cost.
If that is okay for you, he then details the planning, calculates the costs more precisely, and submits the building application. After that, he creates the execution planning and prepares the tender for the individual trades.
Then you receive offers. At this point, you then know pretty exactly what to expect.
You can accept the offers and the trades start building, preferably under the supervision of the architect.