What’s the point? The OP writes that they currently live very cheaply at 580 euros warm, but unfortunately the apartment is too small with a child. Presumably, a larger apartment at current market prices would cost around 1,000 euros.
The small amount of equity that could be saved would surely dissipate over time due to rising prices.
Therefore, plan critically... keep a household budget....
Are there any other liabilities, debts, or car loans?
With 3,500 net income, a 1,000 euro installment should be manageable. Childraising time can possibly be softened somewhat if you arrange interest-only years with KfW. All just food for thought... the deadline is anyway the construction obligation due to the land purchase.
Exactly right, for a child-friendly apartment in a comparable location we would probably have to calculate more like 800-900 euros cold rent. And actually, we would like to build as soon as possible, because then we would live near my parents again – which is also not an insignificant factor when childcare comes into play.
In my current calculation, the 1,000 euro installment would be easily manageable with 3,500 euros (2 salaries), and even with about 2,700 euros (1.5 salaries) it would still be barely feasible. With reserves for house, car, vacation, and my estimated additional expenses for a child, it would then be very tight, but doable. My preferred option would therefore be a loan where at least two repayment adjustments are possible. Then, in an absolute emergency, we could still reduce the installment. A longer term would of course be unfortunate, but in our case, not the end of the world. We are still quite young and have several good working years ahead of us.
Our actual situation is also a little better than what we are calculating. He additionally receives shift allowances, and I earn a few thousand euros per year from self-employed side work. Salary increases are also likely. None of this is something to count on, but it still makes me confident that we can manage the installment in the long term.
Oh dear, 300k might be quite tight. Have you already aligned your wishes with the development plan? You might then end up with 3 floors with living spaces and therefore over 140m², because less doesn’t make much sense. A house with 7x7m doesn’t look very good either.
Also, the exterior facilities with retaining walls and stairs can be relatively expensive.
The development plan gives us considerable freedom. Because of the slope, the plot is also designated differently – on the valley side, we can exit the basement at ground level. Ideally, we want two full floors (130-140m²) plus a usable basement with a shallow pitched roof. But we will have to see at meetings with construction companies whether this is really the optimal solution and whether other floor/roof shapes might not be significantly cheaper.