Single-family house with 2 residential units for KFW funding

This is not a clever question. From my point of view, this question is more like starting the selection of a car by the number of cylinders.

What I mean is:
Unless you are doing the masonry yourself, completely different questions are in the foreground.

Among other things:
Development plan
Surroundings (soundproofing can also be an issue)
The best is a company that fits you personally (one should never give a company the stone beforehand! They should install what they always install and have experience with. The two questions before are only preliminary because they can influence the choice of the company. For example, if clinker is specified and a company has zero experience with it, another one would probably be better suited).

So. Here you still do not have the questions about which company itself is the right one.
Which in turn depends on the plot and the planned house.

Therefore: the stone question is actually not even relevant yet.

If you want to build EH55 (for which there is no KfW anymore), you are better off building monolithic also because it is cheaper...

Our neighbors are currently renovating the facade insulated in the 1990s. Completely removed and done all over again.

You can, if you want, simply insulate over it. Since the old insulation is probably not very thick, that's not a problem. Only the old plaster should be in good condition. But you can also make life difficult and expensive for yourself.

THANKS!

How or with what are you insulating your roof, I’m curious?