Yes, indeed, that would probably reassure me. 5000 EUR plus child benefit would probably be enough. Maybe my worry also stems from our previous circumstances. We have only been working for a relatively short time. We haven’t had the salary and the great division of 70 and 80 % for long. Until the end of parental leave for K1, I was the sole earner because my husband was still completing a second degree. After his second degree, my husband took 6 months parental leave and I went back to work full-time. Then I was on parental leave with K2 quite quickly (9 months after I returned to work after K1), but after his second degree/parental leave, my husband worked full-time again. After K2’s parental leave (9 months after birth), I did not return to work, partly because at that time my husband could not reduce his hours yet. I only returned to work shortly before K2’s 2nd birthday, but back then I was paid less. At the same time, my husband reduced to 80%. Seven months ago, I was promoted, and only since then has our salary been as described above. But I also know other times.
It sounds like everything is just moving a bit too fast for you. A phase of stability might be nice? With house building and K3 in the pipeline, that prospect is currently not given, of course. Maybe build a year later – the plot won’t run away, but building might become more expensive.
Afraid of refinancing? Most people first tap their buffer, if existent, or cut back on the garden budget, if existent. Or delay the garage. Or buy at a fixed price. You can also sell the plot and instead rent an existing property to avoid the risks of new construction.