General procedure / schedule

Hello,
we want to build a Kfw 40 plus house with a prefabricated house provider that is not yet determined. Some elements, such as the photovoltaic system including battery, the prefabricated basement, the garage, the staircase, and possibly a few other points, will be outsourced because it simply makes more sense.
Now to the actual procedure (after purchasing the plot).

1. Search for an architect/energy consultant or will this be handled by an architect from the prefabricated house company even though the basement, photovoltaic system, etc. are ordered externally?

2. Search for an expert who simply supports us during construction. Should we rather take someone from the Bauherren-Schutzbund or someone like the "prefabricated house expert"?

3. Obtain offers from the prefabricated house companies, the basement builders, the photovoltaic system providers, etc. For this, I have already created a list of points so that not too many additional costs appear during the selection process but are included in the first offer (otherwise it would be difficult to compare). Of course, we will conduct a pre-selection to be absolutely sure. What is a sensible order here? That means first prefabricated house provider, then basement builder, then photovoltaic company, then [Ausbub], then staircase builder?

4. Decision on the prefabricated house company and revision or extension of the contracts such as the construction service description through additional clauses and everything that is not fairly balanced.

5. Then the price negotiation. Should professional help also be sought here and if so, whom? Would that person then also be involved?

6. Signature and start signal for the house construction. The architect should have the floor plans etc. ready for the building permit beforehand.

It would be great if a lot of input comes together here so that we are better prepared! Many thanks in advance!

Input: Why prefabricated house, why KfW 40+?

because it simply makes more sense

Which would be? The major prefabricated house suppliers will only credit you ridiculously small amounts here, which would never be sufficient on the open market.
In general, your post sounds more like open contracting than prefabricated house.

Prefabricated basement [...] outsourced

Only a few large prefab house manufacturers participate in this.

The architect should then also have the floor plans, etc. finished beforehand

Not all prefabricated house companies participate here either. Architectural services are only provided after signing. The overlap with outsourcing the basement and the preliminary stage to the building application before contract signing, if it exists at all, is likely small and accordingly exclusive.

Sounds like you want to dictate your rules to a prefab house provider. They will immediately decline and wish you all the best on your further journey. What do you expect from a prefab house provider? An architect (preferably experienced in kfw40+) and then individual contracting fits your ideas better.

We want to save energy and also be a bit more self-sufficient (for that, photovoltaic systems including storage). For me, that also includes ecological insulation (e.g., wood fiber). Keyword: transmission heat loss. And in the end, there is €30,000 as a repayment grant and, through the funding, also better bank conditions. There are certainly more reasons in favor of it. Well, hardly any prefab house company builds the basement themselves but rather commissions external service providers, and then they add 10-20% on top. After all, I only want to use certain services, and that’s ultimately what it is. Simply a selection of services. Since I don’t know what such a path could look like, I wrote the list. So if anyone has a more sensible way, please give feedback.

Of course I only want certain services and not to pay 10-20% more for subcontractors. I hardly believe that is the case, after all, it’s about money and not a small amount. Or do we have a complete saturation of companies? Hmm, I expect that through a FHA the construction of the house only without basement and photovoltaic system including storage and garage (which we want to build a bit later anyway). We can still think about the rest (i.e., external staircase assignment, etc.). So I don’t think these are extravagant wishes, or are they? Actually, it’s about the order.

I don't understand your response to my post, or rather, I don't see the connection. What do you want to pay 20% more for? That you expect a prefabricated house provider to build you a house is obviously logical...

What I mean is that a basement commissioned through a prefab house provider and accordingly outsourced costs 10-20% more than a basement I would commission directly from the basement builder. Since I want to keep these 10-20%, I of course dictate some points in the house construction plan. And I don't believe that the prefab house provider will let us go just because I commission the basement externally. If it is clear what I expect from this, then I don't understand your question. Please explain again. Thanks!