Is financing with this income realistic? Experiences?

Addendum: with €370,000, everything is really taken into account (including 10% contingency). Planned living space approx. 250 sqm (+ 40 sqm garage), 2 full floors on a slab (without basement), complete underfloor heating with water-bearing fireplace, gas boiler, and 4 modules on the roof. However, I was rather thinking of KFW 55 (bricks filled with insulation). Or does another financing concept make more sense?

Addendum: with €370,000 really everything has been considered (including 10% safety margin). Planned living area approx. 250 sqm (+ 40 sqm garage), 2 full floors on a slab (without basement), complete underfloor heating with water-carrying fireplace, gas boiler and 4 modules on the roof. However, I was rather thinking of KfW 55 (bricks filled with insulation). Or does another financing concept make more sense?

I would now just say with 230 sqm + garage 'only' KfW 70 and without 10% reserve, the €370k roughly fits.

I would now simply say that with 230sqm + garage 'only' KfW 70 and without 10% reserve, the 370k€ roughly fits.

I agree, but rather without garage. The heating is quite cheap, as it is a gas boiler. Equipment is average. KfW 55 is likely to be significantly more expensive, the garage also costs money.

Hmm, 250sqm is quite a lot. My entire extended family also has houses of that size - all renovated old buildings. What they all say consistently: If they were to build new, they would all build much smaller. The much unused living space would only be ballast and serve solely to accumulate junk. I mean, if you don't have some unusual hobby or a company in the house, 250sqm is very ample and maybe excessive if money is tight?

By the way, the water-bearing fireplace is very controversial. A stove builder once told us: "A fireplace always remains a luxury and is not suitable for actual heating." We had the idea at first too and then quickly discarded it.

Key data: 1st income: €2350 net; 2nd income: €1550 net;
Marital status currently childless, but planned within the next 2 years;
Plot (developed) is available (value: 1200m² at €75 each);
Equity: €80,000, total costs (incl. house, garage, garden): approx. €370,000.

I was thinking of paying it off with a 20-year fixed interest rate. What is your opinion? Is this possible?

Addendum: with €370,000 really everything is considered (incl. 10% safety margin). Planned living area approx. 250 sqm (+ 40 sqm garage), 2 full floors on a slab foundation (without basement), complete underfloor heating with water-conducting fireplace, gas boiler and 4 modules on the roof. However, I thought more of KfW 55 (with insulation-filled bricks). Or does another financing concept make more sense?

Honestly. I don't think this will work. You would be overextending yourselves.
In the current situation it is possible, but at the latest when you want to have children, it will become tight.

Your total net income: €3,900 - later the salary 2 will be lost for an indefinite period or will be lower (e.g. part-time work) with simultaneously higher expenses.

Your financing wish:
€290,000 with 20 years fixed interest rate and repayment within 20 years.
I don't know exactly where the interest rate is at 20 years (you would currently just miss a 60% loan-to-value ratio), but I estimate it will be around 3.50%.
To be finished within 20 years, you need a classic financing with 3.50% initial repayment - that means an annuity of approx. 7.00%.

€290,000 x 7% = €20,300 p.a. or approx. €1,690 p.m.

And now realistically consider whether this is feasible with only your salary once your child is born.

You are planning a very large house (250 sqm). You should maybe think about making it a bit smaller (150 - 200 sqm) and choosing KfW70. You have equity others would do anything for. If the construction costs go down, you will also reach the 60% loan-to-value ratio and can expect a better interest rate.

...And now realistically consider whether this (once your child is born) is doable with only your salary. You are planning a very large house (250 sqm). You should perhaps think about reducing it a bit (150 - 200 sqm) and opting for KfW70...

What would also argue in favor of downsizing are the ongoing costs for a large house. All the rooms need to be heated if you want to live in it. When planning for children, money gets tight.