Variable or fixed financing for land?

If I were you, I would carefully plan the financing again. 350k€ is about 1500€ monthly installment. In my opinion, that could already be tight with your income (even with the then 3600€), especially if almost 2000€ for the house and additional costs are gone including ancillary costs.

especially since 350k for construction and land in BW is ambitious

In addition, this is almost impossible, and [Garage + Außenanlage] will probably be added on top.

especially since 350k for construction and land in BW is ambitious

That's why there are the cheap offers from Massa Haus, Danwood and from Poland. In my opinion, is overestimating things here. If all goes well, it might just work, but woe to anything going wrong.

SaZ = soldier on a fixed-term contract? Is the job permanent? What about transfers?
What does the income look like after parental leave? How are the daycare costs for you, etc.?

oh dear...

So there have been some changes in the meantime :-)

The equity now amounts to €60,000, since we had 3 cars and actually only need one or rarely two, I have now sold my dream car.

From the bank we therefore only receive and need just under €300,000.

Land, notary & land transfer tax amount to €135,000 for 379m³.

That leaves us with €225,000 for the house, foundation slab and incidental construction costs. The whole thing should now also be directly financeable.

I am SaZ 25 and have 19 years left to go ;-) I am not at risk of reassignment in my post, I have a pretty secure and permanent position.

P.S: I am still self-employed part-time in the IT sector, through which I earn about €300-500 per month, but unfortunately that cannot be taken into account again because I did not pursue my self-employment last year and only started properly again this year with fixed contracts in a company.