Is financing a single-family house feasible for us?

The point from my perspective is the following: If 470k suddenly becomes 600k, €1800 quickly becomes a €2200 installment. Then you have your first child in 3 years and from the wife's €2500 salary, only €1600 remains (part-time). And from the €1800 buffer (which I consider optimistic), suddenly only €500 remain. For me, that would be too tight. I would scale back and leave out the basement and garage.

But really €600k for an 8x10m house with a lot of own work? We could get that cheaper turnkey without any own work.

what do you expect here now? You don’t want to post offers/calculations, the neighbor has already paid 50k more than you are planning. Financing apparently is settled and construction is about to start. You can’t get any advice like this. Based on the information so far, it seems everything is planned with rose-colored glasses.

The forum is tendentially rather negative. Sometimes it is a good counterbalance to the many voices of sellers, etc. Actually, your wife should read all of this here.

You have to be VERY cautious about neighbors' statements regarding the price of house construction. Nowhere is there as much lying as with paid purchase prices and achieved selling prices in real estate.

And I don’t see any cash flow besides the installment. We have lived so far on €1000 per month, why shouldn’t it continue like that. So 1800 installment + 400 additional costs + 1000 living expenses would still be a €1800 "buffer."

So I don’t want to criticize much here that you have lived with your parents so far. Everyone as they like.

But probably EVERYONE had a little shock moment after moving out from their parents. We all thought that we had actually already bought everything ourselves in the end and that expenses would remain the same.

And then you realize that you can’t just plunder Mom and Dad’s fridge if you haven’t shopped yourself. The parents’ car isn’t parked in front of the door if you forgot to refuel. Suddenly, insurances want money that you never heard of before. Electricity, internet, money for a new washing machine, dishwasher repair, other repairs to apartment/house. All things you may have taken care of occasionally but NEVER HAD TO. The annual utility bill, which brought several hundred euros in additional payment.

As I said: nothing against you. You have proven that you can basically save money. The expenses will not break your neck. But please don’t think that you will keep the expenses exactly the same.

Regarding the support from the parents:
Of course, I don’t know your parents. But in my circle of acquaintances, 2 young families relied on the grandparents to care for the grandchild after 1 year.
In Family 1, the grandmother suddenly realized that she cannot just fly on vacation and enjoy retirement. And canceled the whole thing shortly before.
It is really a real burden to care for a one-year-old child all day! (depends on the child)
In Family 2, Corona got in the way. The parents were too afraid of infection.

These are 2 extreme cases. But grandparents often say and like to say that they want to take care of the little ones. You should not rely on that. The good ones also don’t get any younger.

oh yes. One more addendum about the children:

Then you will have the first child in 3 years and the wife's salary will immediately drop from 2500€ to only 1600€ (part-time). And out of the 1800€ buffer (which I consider optimistic), suddenly only 500€ remain.
For me, that would be too tight.
I would scale down and skip the basement and garage.

What is somehow discussed far too rarely here besides the lower salary:
Be SURE to also inform yourselves about daycare fees.
We currently pay 500 euros plus food money every month for U3 care.
It will only decrease in the Ü3 stage. But then still over 300.
Maybe you are lucky and live in a community without fees..

However, with children there are still other benefits: Depending on the pay grade, about 120 euros more salary (gross) and (currently) from the 13th to the 36th month of the child's life, 250 euros Bavarian family allowance. In addition, child benefit of 200 euros, and you quickly reach over 2100 euros again.

From my point of view, it is especially important not to overextend oneself at the beginning and to set clear budgets. Also, watch which subsidies you might be able to take advantage of. The BAFA provides up to 17,500 euros back through support for efficient heat pumps (and jointly controlled controlled residential ventilation). KFW could also become interesting through the repayment grant.

I'll just jump in here and ask the simple question: why do you need a basement? The washing machine is better upstairs, near the clothes. Supplies can be stored in a tall cabinet in the kitchen. Hobby equipment can be stored in niches and well-planned storage space. Also gladly under the ceiling (ideal for surfboards, for example). The party in the party basement has been over for X years. It can also take place at the dining table and ends up in the kitchen anyway. There is simply no very good reason for a basement, except for a hillside location.