Renovation of a 1960s house: Questionable expert recommendations?

And, have you continued with the project?

We had the notary appointment yesterday and are now the owners.
At the moment, we are trying to get potential general contractors who cannot start before 2024 onsite to take a look at everything. First of all, we need to clarify which KfW standard we want to renovate to and how/if the issue of a "second residential unit" can be resolved concerning the funding/subsidy matter. We assume that the major renovation will start next summer.

For now, we are busy freeing the garden from waist-high grass and the garden shed from rampant ivy... :)

First of all, it needs to be clarified which KfW standard we want to renovate to and how/whether the issue of "second residential unit" can be resolved with regard to the funding/subsidy topic.

Then have approved energy consultants come along in parallel or right away. They will quickly be able to tell you what is easy and where a lot of effort is to be expected.

Then have certified energy consultants come in parallel or first. They will quickly be able to tell you what is easy to do and where a lot of effort is to be expected.

Thanks, but I’ve already had two of those. The problem is that apparently anyone can list themselves as an "expert," and it’s hard to tell over the phone what they’re really like. The first was a major saver, wanted to install a gas boiler, leave the old pipes in, hang radiators in the basement, and skip the insulation (see beginning of thread) --> for nothing The second was somewhat more thorough and not quite stuck in the Middle Ages, but gave the blanket statement that a house from this era should "definitely not" be renovated better than KfW100 --> Uh, yes..? Both were such that I felt that despite extensive explanation, first, they didn’t grasp what we actually intend to do there, and second, they apparently don’t often accompany such projects. We don’t want to move in as cheaply and quickly as possible, but to upgrade the place for the future. I don’t necessarily have to achieve the bombastic energy value, but if we’re already starting now, we want to do everything that makes sense now and not start remodeling again in ten years just to have spent a little less now.

Another thing: The aforementioned second expert was on site on 12.05. and pointed out to me due to his workload that his calculations/explanations, whatever he will deliver, would take "two to three weeks." Since then, seven weeks have passed and I haven't heard anything. He also hasn't sent an invoice. Since I expect little from his explanations as indicated above, I actually don't want to pay for them. Should I now just wait out the matter in the hope that he has forgotten me? If he does get in touch later and then sends an invoice very late, can I refuse it with reference to the excessive duration? Or would I now have to set a deadline, with the consequence that he remembers me and still delivers something?

One more thing: The aforementioned second expert was on site with me on 12.05. and pointed out due to his workload that his calculations/explanations, whatever he will provide, would take "two to three weeks." Since then, seven weeks have passed and I haven't heard anything. He also hasn't sent an invoice. Since I don't expect much from his explanations as indicated above, I actually don't want to pay anything for it. Should I now just wait it out in the hope that he has forgotten me? If he still contacts me and then sends an invoice very late, can I refuse to pay it with reference to the excessive delay? Or would I now have to set a deadline with the consequence that he remembers me and still delivers something?

I would address this clearly and directly now, otherwise it could lead to an unpleasant surprise.

We are currently in the process of getting potential general contractors on site who cannot start until 2024 to come and take a look at the whole thing.

I would first look for an experienced architect, they already know the suitable craftsmen.

First of all, it is now necessary to clarify which KfW standard we want to renovate to and how/if the topic of "second residential unit" can be resolved in terms of funding/grant issues.

Then show an inventory, what do the building documents say about plans?