How do you assess this house? How much budget will be necessary?

the energy efficiency class F is also bad.

That is a calculated value that does not say much about the actual energy consumption.

The installer of the freestanding radiator in front of the floor-to-ceiling window deserves a prize!

No, seriously: I read from the OP that he would prefer to build it himself. The house would be a "well, it’s okay too - makeshift solution" due to the lack of building plots. Will one be happy in a makeshift solution in the long run, or will one always be annoyed?

Report back when you have more info. And get informed about what you want. Can you live with normal laminate, a simple gas heating system, and basic radiators, etc., or not. It's really difficult to estimate this. We don’t know you and everyone thinks differently about it. For example, we have laminate, gas heating, normal radiators, simple bathrooms, etc. We can live well with that and our house still looks neat and almost everything has been newly done. With other demands, we could have easily spent 50,000 to 100,000 more. But many things weren't important to us. A simple standard was enough. And our house is much smaller, which also makes a difference.

I also find HZ set too low with 8000 (without HK). Our new gas heating system in the old house already cost 7000 including installation 10 years ago. I also see over 10000. Instead, you can paint ugly brown doors instead of replacing them. If wooden windows can still hold a sheet of paper between the frame and sash, then they are tight enough. Secondary bathrooms can be painted with tile paint and jazzed up with nice towels.

Secondary bathrooms can be painted with tile paint and spruced up with nice towels

Well, really?

Well, seriously now?

Your question is not meant seriously, is it?

Your question isn't serious now, is it?

You can't make such an old toilet nice again in my opinion with just a bit of paint. Sorry, I would put the 8 to 10 grand on the investment list.