Buy an existing single-family house with a large plot and renovate it

Did I understand correctly that there are currently about €4000 left? Where have they gone?

if the house is that big (250sqm living space) do you need it all for yourselves?

the idea would be whether you could make a granny flat (50-90sqm), which could then increase the income further and thereby cover part of the installment?

For a granny flat, the floor plan must fit. Besides, you then lose the biggest advantage that a single-family house offers and have the neighbors even closer than in a townhouse.

if it is a sought-after residential location, then a developer buys the plot, tears down the house and builds an 8-10 family house with at least 600m² of living space. We still have a shortage of apartments and this will worsen because less is being built.

Yes, if the price and the interest rate are right. At the moment, they are not. By the way, this was the beginning of the end of the bubble at the beginning of the year. Such projects were simply no longer started everywhere because there was no money to be made - and in the end, someone still has to be there to buy the tiny units. And if there is a development plan, it is pointless anyway.

I always wonder how the purchase and renovation of a single-family house was financed in the past. Around the year 2000, we financed with about 5% interest! Are the houses too expensive, are the craftsmen and materials too expensive, are the demands too high?
We are currently renovating/restoring a single-family house that was built at the end of the 70s, according to the first WärmeschutzVO. It can be renovated energetically quite well, and you don’t have to do everything immediately. For example, I have received offers for photovoltaics that were outrageously expensive (to be done later), the gas heating, according to the energy consultant, should run for now, and money should be invested in energetic renovation (new windows, insulating the attic/roof with 20 cm between-rafter insulation, larger radiators, installing underfloor heating if floor renovation is due, insulating the basement ceiling, insulating pipes). All of this is preparation for a change in heating technology to a heat pump. This might already be economically feasible now, but the “maybe” and the current hype don’t seem right to me. Basically, my experience is that you have to factor in a good buffer. Not for rising craftsmen costs, but for things that come to mind, that the craftsmen suggest, and that also make sense. For us, that was about 20% of the originally planned costs.