Assessment of whether house construction and loan installment are realistic or not?

With a lot of EL, it is already possible to realize 500k in the current phase – though with a lot of "standard equipment". It is certainly not a mistake to cautiously estimate 550-570k here. Given the conditions of the OP, this is certainly not a problem.

And I wouldn’t fully allocate the 350k equity. Either keep part of it as a buffer or include the buffer in the financing. We have currently calculated many items well during the construction, but costs always come up somewhere that one hadn’t seen or couldn’t have seen.

If not you, then who ... would, however, calculate much more generously.

See no problem at all. However, I would estimate the construction costs higher and hold back 50k equity.

Thank you for the many quick responses.

If I see it correctly now, the construction costs would rather move towards 550k€ and only "300,000€" would be taken in as equity, then the financing would be completed with 250,000€.

This would leave 50k for "Unforeseen" as a buffer. At the same time, income would of course continue to come in and is expected to continue to rise in the coming years.

We will receive a first detailed price indication in the coming weeks. Next week there will be the architect appointment regarding windows (floor-to-ceiling or not, etc.) and further detailed planning.

Are the €150k for the [Grundstück] financed flexibly? Then you have to stay with the same bank, because no bank will go in second rank and terminating the contract against a prepayment penalty is probably not possible either.

Are the €150k for the land financed flexibly? Then you have to stay with the same bank, because no bank will go in second rank and terminating with prepayment penalties is probably not possible.

Yes, it is and it will also be the same bank. That is already planned that way. Otherwise, full financing solely for the land would not have been possible.