Renovation or demolition and new construction - decision support from the architect?

What would you advise us, how should we proceed most sensibly?

It depends. I am a friend of preserving good substance. But only preserving - moving 17 walls, creating new bathrooms, changing windows, etc. in an old building I mostly find pointless, because that then tends toward "becomes more expensive than new construction." Additionally, possibly with further disadvantages of the old building. I don't know the house, so I neither want nor can help you.

What would you advise us, how do we proceed most sensibly? I was thinking, for example, of now planning both renovation and new construction more concretely with the architect, i.e. creating floor plans, submitting a building preliminary inquiry, obtaining quotes.

If the architect is good, this practically clarifies itself between service phase 1 and 2. Planning two houses "more concretely" is certainly wasted money.

Honestly, I didn’t expect such a clear tendency.

I definitely do not see that here either. I can only join

I don't know the house, so I may and cannot help you.

without facts, no serious opinion.

(and regarding photos + floor plan, please check with us whether that is ok for my better half).

It is unavoidable, any therapy without diagnosis would be negligent quackery. I also advise "against blue tiles" personally in a separate room, if madam is too shy to discuss the house on the internet.

Your frank words are refreshing. Honestly, I didn’t expect such a clear tendency. But I also tend to approach things too intellectually (my wife then slows me down).

Unfortunately, you consider my statement without noticing the context. Of course, you can only judge that if you know the object. You still haven’t contributed anything to that. Unfortunately, you misunderstood the hint.

I find that a pity. Old houses are charming in a very different way and shape the cityscape in a (mostly) beautiful manner. It would be a shame if the cities were gradually torn down. A backlog of renovations is actually quite practical. Then you can plan the major interventions right away and don’t have to be sad that existing parts might not survive the changes. It’s annoying when the kitchen is modernized but the hallway is not. When everything is modernized, but not the room layout. Now you can simply plan anew in a probably very nice house. I’m curious about what you have planned. Definitely keep us posted!

I agree. Quoting out of context makes little sense. Let’s wait and see if more information comes that changes my opinion.

So because you are worried about heating costs, that is certainly an issue, but as an example with us built in 1950, 2 households with a total of 4 people living permanently in about 200m2, 250m2 (partly not permanently occupied). Costs 3000€, last year. Could be more in a stronger winter. We are now probably getting a wood stove. Purely monetarily, I still don't think insulating is worth it for our large house. When the roof is due, we will insulate it, but we will only do the facade if we are forced to.

I actually find the indoor climate better as a previous poster has already mentioned, than partly in new buildings. In summer it is significantly cooler due to the thick walls and ventilating at night.

Is the basement the thermal bridge into the house? (according to the architect, you can also excavate and address the basement exterior walls all around, but the cost-benefit ratio is highly questionable).

This is regularly done for damp basements and doesn't cost that much. Of course, you can't get under the basement floor, but if you're not planning to have an office or something like that there, it doesn't matter. You can also insulate the basement ceiling if there is enough ceiling height.
In the non-basement living room, simply install underfloor heating, then you won't have cold feet.