Single-family house 1,000,000 affordability - monthly installment?

Perhaps I can offer a slightly different perspective here, since we are building directly in Munich and I know very well what it feels like to have to deal with unfamiliar sums of money extremely quickly. In our case, it was even a bit more abrupt, as the background was an unexpected, and in that sense definitely not desired at this time, inheritance from a close relative. We could have chosen to keep "playing it safe," as was once suggested in another thread about Munich, and we would have initially felt more comfortable with that, but in the long run, we wanted to stay in the city (now on the very outskirts), and honestly, you have to move very far away from Munich to even find a noticeably smaller “roll” (i.e., cheaper property). Even in my home district of Erding (Dorfen), which is 40-60 minutes away by car, detached single-family homes cost just under a million euros; the scale of prices here is unfortunately actually absurd now compared to rural areas in other federal states.
So for you, as for us, it's a purely emotional decision; rationally, you already know that you can finance the house through very high equity, a good salary, and expected inheritances (which hopefully will take a long time to come). From experience, I can tell you that you very quickly grow into these new dimensions; to some extent, this is true for every homebuilder—as the mortgage of 200,000 might cause sleepless nights for one person, while in the Munich area it only gets uncomfortable at much higher sums for others. In your position, staying in a rental apartment when you long for a garden and space for the children wouldn’t even occur to me.
Personally, I am more risk- and freedom-oriented and do not like owing anything to others. Therefore, as a couple, we decided to keep bank financing as low as possible, even though the stock portfolio probably yields more returns than the interest costs. The loan is small, comparatively short-term, and we feel more comfortable and freer that way; others shy away from liquidating fixed assets and prefer to pay off manageable installments over 30 years—both are possible and very individual. And regarding “keeping your feet on the ground”: We feel the same way as you do. I now have assets, my partner has had a very good salary for years, yet we are building a very nice but (apart from the location) nevertheless normal house, treating ourselves to extras we really want (fireplace, some nice kitchen appliances, beautiful parquet, high-quality bathrooms, and nice tiles) and giving up things we don’t find worth it or consider overpriced, meaning no KNX, huge glass windows, no wood-aluminum windows, no custom carpentry, and no masonry garage. We both grew up in rural areas and were raised down-to-earth, which means we simply continue to live as before and, just like always, carefully consider what is truly important to us and what actually creates beautiful memories and more quality of life when building the house. If I were you, I wouldn’t worry about automatically losing my footing just because this magical million number is now on the house tab; only a handful of people know the costs of our whole construction project, and to everyone else, we are the same people as before, still shopping at Aldi, driving a beloved 15-year-old VW Polo, and very consciously aware that money can buy things and freedoms, but never happiness and contentment.
To bring it back to the financing: Be proud of your professional success and the associated salary as well as thankful for the financial family background that can always let you sleep soundly compared to many other homebuilders. I would definitely fulfill the dream of owning a house and rather look more closely at the construction costs to gain more security. For example, in planning phases 1-4, we also worked with an architect because we thought our desire for a mix of city villa and American house would require it; in retrospect, our architect barely added anything to the floor plan we created ourselves, so we would have gladly saved the 18,000 euros and three months of planning time. I could never have imagined building with individual contracts in Munich since it takes forever to even get offers and an extra Munich surcharge is added to everything. So if you are still free to decide and do not want a super individualized architect house, I would get alternative offers from prefab house suppliers and regional solid house suppliers, who only add this Munich/Bavaria surcharge once and take care of all the coordination work for you and guarantee that the house will be finished in a year :)

Window costs seem very low to me for a 1 million euro property. We have 83 sqm of window area with lift-slide elements, various glass balustrades, most of them floor-to-ceiling... etc.... and are at 50,000 euros. One of the biggest items on our house. Rationally considered, it's too much money just for living. Emotionally, I believe it is a good investment. Otherwise: take a schnapps, close your eyes, and get through it. Much bigger houses have already been built! There are always risks, but the reserves are more than sufficient so that you don't collapse financially....

Conventional electrical installations for 50K €??? What exactly is included in that? Change quickly or go directly to KNX. At this scale, conventional should not be an option.

Thank you very much for the comments and the really nice tone in an online forum. I know it differently...

Me too. We have a full moon ;) But the headline filters many out.

I find that in our still quite young years (clearly after 30 it goes downhill) this is already a hefty decision.

One would think that money matures ;)
I would, even if it is only for your wife, include part of the equity in the construction sum.
After all, it’s a) about a high construction sum
And
b) about financing it despite existing equity
Screw the fact that the interest rates are lower than the profit from investments: it’s about satisfaction, happiness, and health. With your "financial saturation," one should not equate quality of life with the numbers at the bottom line, but also occasionally be more relaxed with oneself, meaning more focus on values and respect. So respect for your wife, that financing this high amount is financially healthy and sensible, but humanly and mentally it is not!

A general question: Should I move the construction cost calculation to another forum or are there enough critical readers here?

Always just: Your request filters out many users.

Obviously, sums like these make you feel sick at first. The situation easily allows for this. It also makes sense to let the equity (except for the land) continue to “work” and finance externally. Whether you want that is something everyone must decide for themselves. Personally, I would rather invest more equity to pay off faster or simply have lower installments. When signing, you feel like you are selling your soul. After a few months of construction, you handle numbers much more relaxed. You have plenty of buffer for unforeseen circumstances or special wishes. Our house became seven-figures more expensive than what we originally planned to spend. Almost all positions were due to our wishes.

I personally would rather bring in more equity to pay off faster or simply have lower installments.

The reason, of course, as well. There are several factors here, including bringing in equity. I think it is wrong to focus only on profit.