Very interesting discussion, this is exactly what I hoped for with my post here! :) Many thanks already to all of you for your very constructive suggestions, thought experiments, and (personal) opinions and experiences.
I already thought that there would be both pro and con contributions here. I understand both sides, especially all those who currently refrain from building and do not want to take the risk. On the other hand, like , I also think that together we have a current net income of about +- 5k, and we are certainly not exactly poor with that. The question is how salaries, living costs, and construction prices/construction interest rates will develop in the next 18 months, which currently no one can predict.
We will now simply watch, wait, and pay down the land, and then see where we stand in 12 or 18 months. If we then go to the bank or to advisors and we are told "no, sorry," then that's just how it is; the land goes back and we have learned from it. If it works out by then, it would be nice, and if we fit with a suitable rate, we would also like to build. With my partner, it is planned that he will be promoted to team leader next year, but at the latest in 2024 — of course not yet fixed in writing. If that works out and we move towards a 6 - 6.5k net household income, it would also look somewhat different again. Provided, of course, that living costs and construction costs etc. do not rise by the same factor. But these are all still thoughts about the future; in 18 months, so much can happen. :)