That sounds interesting, show us some of it.
I’m with you on that, no pictures online, sorry
That’s why I’ve already contacted three energy consultants
Unless they are architects who also work as energy consultants (by the way, not every "energy consultant" is certified to support KFW efficiency houses), they will at most be able to tell you something about energy-related measures. And even if they happen to have a bit more experience with the construction sector (not chimney sweeps ), they will at best give you a rough estimate without guarantee (!). In case of doubt, there are more reliable statements here in the forum.
If anything, you need an expert for building damage, or an architect with a few decades of professional experience under their belt.
But if you really want to turn the place upside down, I wouldn’t worry too much. Check the basement for moisture (loose/missing plaster, peeling/new paint, fogging, musty smell, etc.), also check the roof for damage in the framework caused by insects and the facade for large cracks (including those that have been repaired).
In my opinion, that’s about all even someone with expertise can check without damaging the structure, and most components will be replaced anyway.
Or does it matter to you whether the expert would still leave the windows in for another 10 years?