Frankfurt am Main - Ernst May House - What awaits me?

I can do a lot myself (tiles, ceilings, walls, etc.), but when it comes to gas and electricity, a professional of course has to be involved. I was thinking about 80 - 100k for the complete renovation. Or is that set too low?

double-glazed aluminum windows from 1975

They still last forever, but this should still be a single-shell generation, so without separation of the profile into outside and inside.

They still last forever, but this is probably a single-layer generation, so without separation of the profile into outside and inside.

what exactly does that mean? Can it be somehow insulated or is it best to replace it directly?

So the windows need to be replaced. They are anything but up-to-date. What ELSE MIGHT come up:
Front door
Electricity
Water
Sewage
Roof
Floors (possibly asbestos because renovated in the 70s?)

Depending on what is done, the above-mentioned things already amount to well over €80,000. Generously estimated.

what exactly does that mean? can it be isolated somehow or is it best to replace it directly?

If they don't have the separation yet, only replacement is possible.