Buy land with cash, construction through KfW/NRW Bank

We have calculated €4000 every month for loan + operating costs, car, insurance, groceries, etc. My partner would then "only" have €700 left - we do not have a joint account and do not plan to - everyone puts €2k into the household account then.

That is generously calculated with the €4000. But you have the salary and so in the end you save what you don't have to spend for the house. That’s already good. However, I think that with a ratio of 3900/2700 you do contribute more. For example €300, so that then €1000 remain.

You then contribute more to it. For example 300€, so that you then keep 1000€.

I understand the line of thought, but here it must be added that 95% of the equity is mine.

I understand the line of thought, but you have to add that 95% of the equity is mine

That may be so, and that is then also contractually secured (my suggestion). However, living long-term on €700 a month (when you can actually afford quite a bit with the good €2700 salary) can be quite wearing and unsatisfactory. If this €300 or then €600 difference is a problem for you with a €3900 salary, then you should reconsider a joint house. Because latent (i.e. intangible) dissatisfaction can also lead to a breakup quite quickly.

700€ in the long run

That would only be temporary, she only started working full-time 8 months ago and that is her starting salary, in 1-2 years it will be higher again and it will take that long anyway until you move in, I think. I currently pay more things out of my own pocket for that.

Spoke again with the financing advisor, he said again we should buy the land and use it as equity. If necessary, take out a small short-term loan if we can't manage to get the rest by the deadline. It would be much better for the conditions. He currently calculated with 3.3%.