House financially feasible at about 5,000 net?

You did not miscalculate. However, variables are missing in the calculation. The cars require tires, maintenance, and repairs. For us, the cars incur almost identical costs of 115 EUR per month for fuel and 205 EUR for their maintenance. EDIT: But it was quite an unfavorable comparison period, in which major services and two sets of tires were due.

However, there are supposedly people who do not have comprehensive or partial insurance and do the maintenance or repairs themselves or have a friend do it for a case of beer. Although this is off-topic, the spare parts cost between 10-20% of dealer prices on the internet and still only 30-40% of those from an independent workshop.

PS. when it comes to financing, it's best to make sure you can switch repayments. Until the children arrive, you could take higher repayments, then lower them for the few years when the children come, and when the second income is back, adjust them upwards again.

I always find it a bit strange, repayments up, repayments down, and if something unexpected happens, you have to crawl back and hope. Of course, it teaches discipline when the money is gone right at the beginning of the month, but personally, with a tight budget, I prefer the option (several banks offered us the choice of repayment switches or special repayments without additional costs) to choose minimum repayments with the option of special repayments. This naturally requires more self-discipline to save and really set aside money over the year, but I have the freedom to shape each year that way. Leaving interest losses aside.

Fundamentally, I also consider it manageable within that framework, the savings rate seems realistically good and not just calculated. Looking for a plot of land and saving as much equity as possible on the side to improve the loan-to-value ratio and thus the interest rate. If in doubt, I would then have it specifically calculated whether it might make sense to "sacrifice" part of the stocks and save them anew in the following years.

So the bold plan.
I don’t want to tell you that it’s not doable.
But from experience, I can tell you that the world looks completely different with children. To put it bluntly, the child definitely decides when you can go back to full work again.
As mentioned at the beginning, the parameters fit for you anyway at first glance. I just encourage you to think more carefully about life with a child. For reasons.

With friends of mine, "she" is a dentist and "he" a carpenter. It’s an easy decision who takes a relatively short parental leave and then goes back to work full-time and brings the money home. Both are happy with it. Occasional sideways glances from others just have to be ignored in the year 2022. And if people already assume that a daycare / kindergarten couldn’t work, then no one would be allowed to build.
Equity could be a bit higher, but otherwise those are good conditions.

I always find it a bit strange, repayment up, repayment down, and when something unexpected happens you have to crawl up and hope. Of course, it teaches a lesson when the money is gone right at the beginning of the month, but personally, with a tight budget, I prefer the option (several banks offered us the choice of changing repayment or special repayment without additional costs) to choose the minimum repayment with a special repayment option. This of course requires more self-discipline to save and really set aside money over the year, but this way I have the freedom to design each year. Leaving aside interest losses.

Basically, I also consider it manageable within that framework, the savings rate seems realistic and not just calculated. Looking for a plot of land and saving equity on the side to improve the loan-to-value ratio and thus the interest rate. In case of doubt, I would have a concrete calculation done to see if it might make sense to "sacrifice" part of the stocks and save them anew in the following years.

Honestly, I don’t find that strange at all – rather, the loan is simply tailored to the living situation so that the quality of life does not suffer extremely.

At the age of the prospective homeowners, it’s quite reasonable to do this for the first 2-3 years with the children to have more flexibility. Logically, you then have to adjust the repayment rate again – but I trust the poster to have enough self-discipline for that.

Often, you get about 4 repayment change options during the term, so with 2 children you can change it twice. We also have that included – whether we will use it, we will see – but the possibility exists, which is often crucial for the sense of security.

so they are still relatively young, i.e. if they take out a loan now, they can also afford a repayment of 4% or more per year after the construction (in 12-18 months).

for the transition period when children arrive, it is reduced to 2% (or even less).

and there are banks where you can do this kind of thing quickly and unbureaucratically online yourself, without having to run to the bank, with 2 clicks...

Our rough plan was full repayment in 30 years, we would also like to work with special repayments.
At 40 years I really couldn't sleep anymore, same with 500,000 euros.
We have not dealt with the change of repayment yet.

And again about the car: we can also assume 300/month here with wear and tear (excl. savings rate)