Financing - which construction financing is sensible?

Therefore you do not pay it off alone. You can only generate what you generate because other work is kept "off your back." Thus, your wife provides an immaterial contribution to the repayment. That’s it.

The situation is different if (still) no children are present.

Seriously? If my husband had approached me like that, I would have shown him the door. Excluding your partner from life planning from the start. That clearly shows how much you trust the relationship.
By the way: I pay off our house completely on my own. My husband doesn’t pay a single cent, but he is involved 50%. We are a couple and act as such. Everyone contributes to our shared life what they can.
Oh, and your personal insolvency... don’t worry about that, the house can be sold then. Since you will have paid off some by then, you should at least break even.
Besides, you intend to finance the house alone anyway (that’s what you really have to be able to manage for the bank). So it doesn’t matter whether your wife stays with you or not.

I met her six months ago while I was already planning the house construction. I informed her after four months and include her in all points (decisions). I do not live with her because she lives with her parents. Under circumstances, if we were to marry and have children, I would be the last person to deny her a 50% stake.

If I am married to someone and have children, that would be a completely different basis for decisions (from my point of view). I would never have asked this question then.

Regarding your financing, I can only tell you what I felt comfortable with myself.

My financing consists of 3 components: a 20-, 15-, and 10-year loan. The advantage here is that the monthly burden decreases in these 3 phases, compared to repaying over 20-25 years.

This means that after 10 and 15 years, the payments for the two loans cease. With special repayments even earlier.

Thanks! I'm leaning almost towards 10 and 20 years. Although maybe it's better to make extra repayments on the 20-year one, since it has a higher interest rate. If possible.

I met her 6 months ago while I was already in the house building planning phase. I brought her in after 4 months and involve her in all points (decisions). I do not live with her because she lives with her parents. Under circumstances, if we were to get married and have children, I would be the last person to deny her a 50% registration.

If I am married to someone and have children, that would be a completely different basis for decision-making (from my point of view). I would never have asked this question then.