You have at least, in my opinion, calculated conservatively. But I consider around €2200 per sqm of living space to be at least too much for what was mentioned!
The trench collector, after deducting the subsidy, costs from experience almost as much as an air-to-water heat pump. You don’t have a basement. No elaborate terrace windows are planned. No significant secondary construction costs according to DIN 276, since you don’t have an architect. You will apparently handle everything yourself. There are no challenges with the outdoor facilities and no plans to invest a lot of money here.
We will build around Nuremberg. That means we also don’t calculate as if we were living in MVP. But that seems to me to be about €30-40k too high.
So this high calculation comes first?