What financial framework is possible for the planned house construction?

And if I take care of the child and she has to live somewhere in Saxony-Anhalt for her ref, then we can get by with 1400 net?

With tax class 3 it should be a bit more. And maybe you can do a little part-time work on the side, or work from home or something like that. These few years of sacrifice will pay off very quickly for her (apart from the other benefits as a civil servant). With another education provider, or as a research assistant at the university, she would never get as much net as she does as a civil servant. This is about her lifelong income! You can’t make that dependent on a property worth €7,000...

So, my opinion on the situation is that the financing works, even if you don't get married and your girlfriend's income drops to zero. I would consider that a worst case, which can already be financially mitigated by marriage.

The plot including demolition costs as much as a garage, the house without a basement has a manageable sum, certain savings are already there.

I see no reason to save further and wait.

For us, however, moving to the other end of Saxony-Anhalt just because there might possibly be a position waiting there is not an option. What am I supposed to do then? Don’t get me wrong, I wish my girlfriend every job in the world. However, both need to be happy somewhere. According to your argument, every citizen would have to become a civil servant.... Because that is supposed to be the ultimate.

Strange priorities – you wouldn’t move for her secure position because you wouldn’t have a secure position there, but the other way around is completely obvious? No one has to become a civil servant, and it is not the ultimate for everyone. But for her it certainly is – all other options are not comparable. To your question: of course you can already pay for the house now. It is only annoying for your wife if she doesn’t get a teaching trainee position nearby after all. The resulting expected loss of income will be felt by you as a family and especially by your wife for a lifetime.

Working from home is not possible for me

You are an engineer after all. Working from home should actually be possible, right? What is the problem?

I work in the large sphere of influence of a major northern German car manufacturer. In our company, there is no home office. I am practically an applicator, so it is indispensable that I work on the car there. I am actually not worried about my girlfriend’s [ref] and the location; we should manage that somehow. Even if it will be 1.5 hellish years. However, it is out of the question for her to move to the other end of S-A for a permanent job. Simply because we have all our social contacts here.

Our plan now is to acquire the plot of land and prepare everything calmly for construction, and only start building the house after her [ref]. Then she will have all the peace in the world to look for something suitable nearby. Even if everything should turn out differently. I can sell the plot of land and, in an emergency, give it away. That would not mean financial ruin given the amount.

Actually, my concern was only to clarify the worst case...

Especially if you work in the sphere of influence of this car manufacturer, a secure salary would be worth its weight in gold to your wife. I live in the city where this corporation is located (and feels like 50% work there), and hardly anyone here dares to make predictions about how the corporation will look in a few years. And the suppliers will be the first to notice.