Financing single-family house purchase + renovation (multiple options)

Isn't it cheaper to rent at those amounts? With your properties, the rent basically pays for itself.

Of course, ownership is nice, but at those prices, in my eyes, there is somehow no cost-benefit anymore...

The property is nicely located on a slope with a great distant view.

Slope + distant view + Lower Saxony + metropolitan area? Not much comes to mind, at least not the Hamburg metropolitan area, which I initially suspected.
South of Osnabrück, southwest of Hanover, or the slopes west / east of Göttingen.
I have now looked at the price levels for all three areas and, no matter how hard I try, I can't construct your price.

- near-city 1200sqm plot with a semi-detached house needing major renovation on it. Purchase price 690,000 €, the seller was not willing to sell for 650,000 €. Even after it came out that it would be better to demolish it, there was hardly any willingness to negotiate on the seller’s side.

Demolishing and rebuilding a semi-detached house is always very difficult and expensive if the other half must remain standing. That would be another drastic devaluation of the property.
You don't know at what price it was ultimately sold. Maybe the realization came later? Just go by and ask the new owner. Many are quite talkative there. Or check your extract from the appraisal committee. However, I don’t know if the case will already be registered there. In the municipalities I inquired about, notarizations were included that were only a few weeks old.

- for the current property, the sellers credibly say that they had 13 viewings over the weekend and at least 5 (that was the status on Monday) are coming again this weekend with an expert.

The large number of viewers does not surprise me. Many buyers by now have adjusted to the fact that many listings call out fantasy prices. They still go to the viewing, just to be in the running at first.
This is also confirmed to me by fellow interested parties whom I meet at viewings. Mass viewings are happening again these days as well.

- renovated house from the 60s (renovated in 2004, so almost 20 years ago), similar but worse location than the current property. Estimated purchase price: 1 million € – no response to a query about room for price negotiation.

And? Sold?

As I said: Have your bank appraise the place. That way you will find out what is also being told to your competitors about the house – and so you can better estimate what they are willing to pay.

4) What would be the smartest way to compensate my girlfriend? - She gets more shares in the new house? - I pay the loan alone and she invests the saved amount and we remain equally listed in the land register (equity share is almost exactly 50/50 without the house, loan amount ~ house sale proceeds) - Other options?

I have struggled with this issue for a long time as well. My insight is as follows: As long as you get along well (which I wish you lifelong!), it doesn't matter at all who is listed as the owner in the land register. If you no longer get along (which one wouldn't hope for, but must not overlook), then there is nothing worse than both partners being owners. Then the house quickly falls victim to a "Rosenkrieg" (acrimonious separation), goes into forced auction, and in the end neither of you gets it. On the other hand, there are no advantages to joint ownership, because: see above (as long as you get along). I no longer have a clear overview of your impressive portfolio of financial and physical assets as well as the enormous inheritance avalanche rolling toward you. But can it somehow be arranged that only one of you buys? And if he/she cannot make that decision alone, you can always register a right in the land register for the money contributed by the other. Then, in the tragic event of separation, this fixed amount would be paid out and then there is peace—without an auction. All this is an uncomfortable topic, but better to clarify it now.

Even if the house is sold, both benefit together from possible increases in value. Nowadays, hardly any families can afford a house on a single income. Furthermore, this has already been discussed here in the forum (and certainly happens quite often): the house belongs to the husband, the wife raises the children and, in case of emergency, has exactly nothing.

Isn't it cheaper to rent something given the amounts? With your properties, the rent basically pays for itself.

Of course ownership is nice, but at those prices, in my eyes, it somehow no longer makes economic sense...

Well, it’s not like rents aren’t expensive either. For correspondingly large apartments with outdoor space (we currently have neither garden nor balcony), you pay at least 1700 gross, rather more. Renting a house can be completely ruled out, and rents tend to rise in the nicer locations rather than fall (yes, it may be that in X years they drop again – but that’s not foreseeable) – while the mortgage payment remains stable.

I can no longer quite keep track with your impressive portfolio of cash and tangible assets as well as the immense inheritance avalanche rolling towards you. But is it somehow possible that only one of you buys? And if he/she can’t sign alone, you can always register a right in the land register for the money contributed yourself. Then in the tragic case of separation this fixed amount would be paid out and that’s it – no auction.

All that is an uncomfortable topic, but better to clarify it now.

Basically, it’s quite simple: she has the assets, I have the income. So it becomes difficult if only one should buy (I would have to pay off 900K € loan alone (no way...) and she about 200K – which probably wouldn’t work with 1100 net monthly and no rental income :)). Registering rights is a good idea. We wanted to see a lawyer anyway when the time comes.

The nice thing is that we can talk about it very openly and calmly without problems – at least as long as it stays theoretical as before :) But that is certainly partly because normally neither of us has to worry much about old age.

Slope + distant view + Lower Saxony + metropolitan area? Not much question, at least not the Hamburg metropolitan area I first suspected.
South of Osnabrück, southwest of Hanover, or the slopes west/east of Göttingen.
I’ve now looked at the price levels for all three areas and can’t possibly construct your price.

As I said: Have your bank appraise the house. That way you find out what your competitors are being told about the house – and you can better estimate what they are willing to pay.

The slopes also exist directly in Göttingen city. Everything east/southeast of the core city center goes uphill. You really have to not underestimate that the city is home to Sartorius, an extremely growing, very well-paying DAX company that has benefited greatly from the pandemic (a few years ago they had 3000 employees, now 10,000 – of course not all here, but there’s also significant increase here) and also a disproportionately high number of high earners through the university are in the arena. Then you add an inheritance as we do and you can afford something like that. The problem is simply the virtually non-existent supply because almost nobody is currently selling. I also thought at the beginning of our search that we would easily find something with the budget, but unfortunately no.

I believe, except for the semi-detached house, everything is actually sold. Of course, I don’t know at what price in the end, but as I said, after a few years of searching I think we have a pretty good feeling for what is being asked and how realistic that is.

Even if the house is sold, both benefit together from any increase in value.

According to the cases known to me personally, where people lost their house in this way, the aspect of value increase was rather secondary. But of course, there can be other cases—I do not deny that.
Both benefit from the increase in value anyway if they are married and have not agreed on separation of property. If I bring a house worth €500k into the marriage (remaining sole owner) and at the time of divorce it is worth €700k, I still have to pay the spouse €100k. Only this then works without auction.

The house belongs to the man, the woman raises the children and in case of emergency has exactly nothing.

I did not suggest that. And the outlined solution means exactly that both have something in the event of separation.