What is the interest rate lock period in construction financing?

I would go with the 10 years. With Sondertilgung you increase the break-even interest rate again and personally I don’t believe in such an interest rate increase. But of course nobody knows that. However, it won’t kill you if the interest rate rises to 5%, so from that perspective you can bear this risk.

The 0.6 is too expensive. 0.5 or lower is possible with your equity ratio.

The 0.6 is too expensive. 0.5 or less is possible with your equity ratio.

In the long-term area, interest rates have increased quite significantly (which the average consumer perceives as strong).

I don't have to liquidate the stock ETF exactly when they have just fallen; I can do a full refinancing and delay the liquidation.

Point 1 of your ETF/stock explanation is nonsense. If you think like that, you would never get started because in 9 out of 10 years you think stocks are overvalued. That reminds me of a chart with the "DAX unlucky bird" who invested 1,000 euros every year at the peak for 34 years and, because of this bad luck, turned 34,000 into only 111,000 euros. With monthly savings and taking average prices, there is hardly any risk even over a horizon of 10-15 years, let alone alternatives.

The future cannot be predicted. Central banks will surely try to keep interest rates low for a few more years, but the question is how long they can actually do that. If there is an expectation that inflation will come, corresponding bond yields will be expected, and these are crucial for real estate financing. See last week.

Personally, I would go for 15 years when weighing up. The differences will not be particularly large, but at least you have security. I personally do not consider 2% unrealistic in 10 years. And ETF savings plans are basically a good idea but with three caveats. First, stocks are currently relatively highly valued (in plain terms: the long-term average return is only limitedly to be expected because in recent years it was significantly above average), secondly, if interest rates rise significantly (say 3-4%), stocks would fall sharply, and thirdly, stocks are fundamentally problematic if you have to liquidate them at a fixed point in time.

You are misunderstanding something. I never said that you shouldn't get in, and the dumbest thing you can do is wait for the entry. The second dumbest thing is usually to invest all the money at once (exactly what you do with real estate ;)). Savings plans are ideal for the stock market. Set them up once and let them run, regardless of whether the market is doing well or poorly. What I said is that they are overvalued, which is different from being too high. Although some sectors are definitely overvalued (*cough* hydrogen *cough*). This can normalize in two ways: stagnation in the medium future until valuations fit, or a strong correction followed by everything continuing normally. In both cases, the return over a few years is below average (whatever that specifically means and is worth). The best example of this is the 70s: hardly any return from stocks and high inflation. Anyone who needed money in 1980 fared quite badly. However, the 80s were great and the 90s up to the dotcom bubble as well. But this is not the forum to discuss that ;) If the OP is OK with simply refinancing then that’s all good. However, I wouldn’t recommend anyone to build a follow-up financing fixed on the idea that they will liquidate stocks at a certain point.