Is a new building realistic?

4 million out of 17 million have 4500 euros and more, that is about 23.5% (not 14.6) 7 million out of 17 million have 3200 euros and more, that is 41.1% (or 58.9% who have less than 3200 euros)

Of course, nothing further can be derived exactly from the data. But if I know that around 6 million households own a condominium (and not a house) and can assume that such is generally cheaper than a house (the few thousand households in metropolitan areas with exorbitantly expensive condos do not distort the statistics that much), I boldly assume that homeowners are found in the upper income brackets, i.e. in the range of 2000 euros net and upwards. Since we probably also agree that you cannot finance a house with 2000 euros net, I further assume that the portion of households at this income level inherited the property.

Hope it is clearer now what I am talking about

Edit: Good night

You will laugh, but we have 50% more tenants than homeowners. According to the Federal Statistical Office, 28% of households can afford their own house. If you also include condominiums, it is still 46%, which means that 54% of households rent.
Nevertheless, I agree with you if you think that 30% of net income is somewhat cautiously calculated. I mean "one" advises a maximum of 45% – the truth lies somewhere in between...

I would say your main problem is outsourcing all positions that cannot be recorded under "everyday expenses." In doing so, you lose sight of how large this item actually is and consequently cannot understand if you can at best be granted a "buffer" of 300 euros.

Just calculate it (I deliberately take low estimated values):

You already mentioned daycare meals --> 50 euros/month
Once a year around the child (clothes, toys, car seat, etc.) at 120 euros --> 10 euros/month
Once a year a new pair of pants at 24 euros each --> 4 euros/month
Once a year a set of tops at 24 euros each --> 4 euros/month
Once a year new underwear and socks at 12 euros each --> 2 euros/month
Once a year a barbecue party for the birthday at 96 euros --> 8 euros/month
Twice a year a good book/a CD (x2) at 15 euros each --> 5 euros/month
Every 2 years a vacation at the seaside: 600 euros AI --> 25 euros/month
Every 2 years a new pair of shoes at 48 euros --> 2 euros/month
Every 5 years a new laptop/tablet/PC (x2) at 240 euros --> 8 euros/month
Every 5 years a new smartphone (x2) at 240 euros --> 8 euros/month
Every 7.5 years 2 sets of new tires at 280 euros each --> 6 euros/month
Every 10 years a new piece of furniture averaging 360 euros --> 3 euros/month
Every 10 years a new TV/projector at 480 euros --> 4 euros/month
Every 10 years a new dryer at 240 euros --> 2 euros/month
Every 10 years a new dishwasher at 240 euros --> 2 euros/month
Every 15 years a new car at 10,000 euros --> 56 euros/month
Every 15 years a new fridge at 480 euros --> 3 euros/month
Every 15 years a new washing machine at 480 euros --> 3 euros/month
Every 20 years a new stove at 480 euros --> 2 euros/month