Log house in solid wood or post-and-beam construction - experiences?

"low U-value = little heating = spending little money" But it's not quite that simple.

But fundamentally, it is basically that simple. That more is involved here is beyond question. However, if you unnecessarily complicate basic principles, you usually have not understood them.

No, it is not. Lower U-values do save dynamic expenses, but they cause significant additional costs in the construction of a building. And these often have a negative correlation, meaning the additional costs do not pay off or only do so over illusorily long periods.

Nope, as you write "low U-value = little heating = spending little money." Amortization is something completely different and less trivial at first. What is currently economical is initially based on empirical values, but you can also calculate it. Economical depending on the construction method is currently a U-value between 0.16 and 0.24. Unfortunately, you have no idea, but that's not a problem if you're not an engineer.

Which U-value is economically optimal is always a question of assumptions, the crystal ball used, and also the respective construction method.
If someone has no idea, it doesn’t matter for the questioner here, because with the assumed construction method: log house ONLY solid wood in the wall, the most expensive construction method with the highest U-value, meaning the worst thermal insulation, comes together. Purely economically considered, it makes no sense. For irrational builders, it then has to be about 30 cm wall made of solid (glued) wood according to the Energy Saving Ordinance.

For log house enthusiasts, the cheapest construction method would be a double log wall structure with two times 8 cm (or so) log beams and insulation in between. The insulation can also be made from jute or similar without chemicals, wood preservatives, and foils. Cheaper is of course also possible with only one layer of log beams and interior panels, but then you might as well not do it and build a timber frame.

I would then not do the timber frame with log beams as cladding, but only with a hung ventilated facade. That can also be done without much fuss with jute and without foil. Price-wise, that probably doesn't make much difference compared to the double log – so rather a matter of religion.

What is "better" ultimately depends on your own motivation: for example, is it about "the good feeling" that your house was knitted by free-range chickens under a full moon?

Once again on the wood topic: old half-timbered houses etc. yes sure, there are plenty of them, but with wood protection, consistently from the beginning. The realization existed hundreds of years ago that some copper/heavy metal slurries were applied to protect the wood from biotic infestation. My point was only that it sounded like TE wanted to set up a completely untreated house. That doesn’t work.