Cost planning - core renovation of farmhouse / country house

Of course. But I think that somehow belongs to such a farmhouse as well. Besides, I have seen some quite interesting (semi-)automatic refilling systems etc. online. When you have space, you can implement all kinds of things.

A masonry stove is also somewhat semi-comfortable to operate if you’re used to heat pumps, etc. :D (I say this as a wood heating user.)

The wood generates heat multiple times: when chopping, splitting, stacking, carrying it to the stove, heating... Semi-comfortable describes it pretty well. There’s just something to do if you want it to get warm, and traveling in winter requires a solution to prevent the house from freezing. For a traditional farmhouse, I think a heat pump won’t achieve sufficient energy efficiency. A pellet heating system or a wood gasifier with automatic feed would be more suitable. I recommend looking at the Austrian suppliers; from my perspective, they are very advanced.

Yes, 150-180 is also often found here as a size. I had calculated with 300k because we have a new build here including the mentioned standards and where the shell construction also had to be done, for around 308k.
But it is a different project, so I have little idea where the costs occur in the renovation.

Keep in mind that demolition and disposal costs are also added and above all that prices are rallying and have risen sharply this year.

that this year prices are rallying and have risen sharply

But you’re playing right into their hands again when it comes to the selling price of your house!

Thanks already for the numerous tips! Of course, it is entirely true that I perhaps shouldn't insist on an air-to-water heat pump. I just want to keep it as sustainable as possible (since we already have a climate) and completely avoid fossil fuels. Gas is also out of the question. But wood, of course, is acceptable somewhere. In general, you can surprisingly well find firewood here in the countryside if you browse through eBay Classifieds. From what I’m learning here about renovation, it would also be an option to look for something really dilapidated that can be torn down to then build a new house. That would be easier in many respects. For example, I found a property around 165k, a reasonably large plot, and according to the ad "almost isolated" – I was already enchanted but then saw that there is a campsite 600m as the crow flies, and I quickly filed it away. :D But generally – larger area in a secluded location for demolition and rebuilding would probably be more like it. What can you roughly expect for demolition costs for an old building?

But generally - a larger area in a solitary location to tear down and rebuild would probably be more like it.

These properties are usually located in rural areas. There's no such thing as "just build something new." Different rules apply. In rural areas (= farmstead), by the way, the core renovation you have in mind also counts as new construction – so with a building permit, otherwise it would be an illegal building. Just so you know ;) .