Larger loan with only 5 years interest fixation

We did exactly the same. Five years fixed interest, 3 components, of which 2 are KfW. All with 5 years. Full financing, but a significantly lower amount.
Back then, interest rates were still a bit higher and the gap to 10 years was still large. We had 2.5% interest compared to 3.3% for 10 years.
After 5 years, we repaid everything and went to another bank, with 6 months forward.
We ended up at 1.4%.
I think it was definitely worth it. If we had taken the 10 years, we would have paid 3.3% for 10 years. That was certainly a *few* thousand in interest that we saved that way. Or a few tens of thousands?

Now, with the second financing (nochn Haus), we took 10 years for the main part. It simply hardly makes any difference anymore. The smaller loan part also again has 5 years, but only because it should also be repaid within 5 years.

What do you think of this approach?

I have not read all the other posts. I find the approach understandable and had similar thoughts "back then." There will only be significant interest rate jumps if the key interest rates rise, and currently the trend is still going down, both in the EU and the USA. Five years go by quickly, the fixed interest period starts from the signature, then you build the house and pay off for 4 years, then it’s time again. And: with 5 years you are always within reach of a forward loan in case you get cold feet. On the other hand, we are currently in a historical low interest rate environment; it’s crazy what money currently (does not) cost.

However, it is important not to use this tactic just because the project would not be feasible otherwise. Then it’s speculation.

Don’t go for variable interest rates. Too few banks offer it and it is sometimes even more expensive than 5 years, because the bank’s refinancing costs must be covered. You could be gone again after one year.

You could be gone again after a year.

... or the bank agrees on an exit fee right away. We do that with all our commercial customers.