Cost planning - core renovation of farmhouse / country house

That does not apply to the OP. She still lives in her house. Maybe she can finance in between. So buy X, renovate, move, and still benefit from the price increase of the current house over the 2 years (or however many) as part of the purchase price. Of course, this requires a good income, such an interim double financing.

I understand that this is currently not the case. But there is the possibility that one cannot finance twice, but must sell beforehand. And that was what I wanted to point out.

Anyway, regarding fiber optic: we also live in a rural area and fiber optic will be installed here soon. Even the entire old core of the village is participating. In other words, centuries-old half-timbered houses will then be up to date with the latest technology!

It is important that the entire TAL up to the IAD is fiber optic. Fiber optic that is "converted" to copper before the IAD is effectively slower technology than copper. Beyond the IAD, it can then, as far as I am concerned, happily be doorbell wire.

Demolition costs depend on many factors. Quantity of construction debris Hazard class Where it will be disposed of

We demolished for 45 k in 2017; if we had the worst hazard class (which occurs more often in barns and post-war renovations), it would have been over 100 k. Barn, tractor garage, stable and residential building. Asbestos was neither extremely expensive nor complicated. Specialist company and done.

Renovation - we quickly discarded that. More expensive than new construction and many compromises. Barn only wood with asbestos roof - conversion to living space not approved or extremely difficult due to proximity to the neighbor. Also, what do you want to make out of a 10m high building other than a wooden shed? Cow stable door, windows nicely curved, there I really saw a living space. Feed chamber had to be removed so that light could come in. Pigsty next door would be slightly elevated. Without underfloor heating or suspended ceilings, the room height would have fit. Upstairs again only wood. Structural stability? Wood would have had to be replaced by a new wall. Tractor garage, cellar above ground - you have to be a hobbit to live in there. Besides, everything would be narrow so that the rooms would be lined up like beads on a string. So away with it

Residential building half simply poured some concrete on the ground, done; the other half built under with old vaulted cellar, wall construction timber framing - with unknown damages under the plaster, ceilings sagged, wooden beams and straw, roof was storage for grain. High enough for living space, no light, no electricity, no water, timber framing, concrete tiles, costs complete interior construction incl. heating/sanitary/electricity + windows + roof + energy measures + building fabric defects + new telephone/electric/water pipes

I am aware that this is currently not the case. But there is the possibility that one cannot finance twice, but must sell first. And that is what I wanted to point out.

I have to admit that I don’t have a concrete plan yet on how this is supposed to work.
The fact is, we have recently been living in the house and are basically paying installments now, no more rent. We definitely want to move from ownership to ownership.
Income-wise, starting next year we should have about 1.5 times as much left monthly as we currently pay in installments. Still, it would only be temporarily possible to cover the double installment; that is already a considerable burden to pay out over 2k per month for installments.

I have no idea how it works to sell property and buy property again.
Is it also possible to conclude a purchase contract one year in advance? So basically find a buyer for the house but say we only sell in "XY next year"? I could imagine there are interested parties for that, but it is not usual, right?
How do others do it/ what models are there?

Read in another thread and also experienced with a colleague: sale now and handover months later. Therefore, I assume that the purchase price is of course fixed now, even if the seller incurs additional costs during the house construction. Otherwise, the procedure is not uncommon.

Is there also the possibility to conclude a purchase contract 1 year in advance? So basically find a buyer for the house, but say we only sell it at "XY next year"? I could imagine that there are interested parties for that, but it's not common, right?

Totally normal. I have done that myself twice in the last 10 years. Then you just live as a tenant for a certain period.