Is financing for house purchase / house construction feasible?

And please consider whether 120m² without a basement is enough for you, that is really VERY small.

I fully agree with that ... you just have to remember, if you currently live in maybe 80 sqm and perhaps also have a basement room, there is a laundry/drying basement and possibly even a bicycle basement, all of this now has to fit into 120 sqm ... and then there is the building services. And suddenly a 120 sqm house is less spacious than an 80 sqm apartment.

I totally agree ... you just have to keep in mind that if you currently live in maybe 80 sqm and perhaps also have a basement room, there is a laundry/drying room in the basement and maybe even a bike cellar, then all of this now has to fit into 120 sqm ... and then the building services as well. And suddenly a 120 sqm house is less spacious than an 80 sqm apartment.

Without a basement, if I put that much money on the table, I wouldn’t build under 140 sqm... Even that isn’t that much.

Without a basement, if I'm putting that much money on the table, I wouldn't build less than 140m²... Even that is not much.

That's how we calculate as well. Although you should consider each individual case. - Is an attic available as storage? - Maybe the garage will be planned a bit larger? - Is a garden shed planned? Basically, you really shouldn't plan too tight. After all, you are putting a lot of money on the table. Usually the biggest purchase of your life. If the house then feels more cramped than an apartment, you haven't gained anything. What can help: Draw the existing/planned furniture into the planned floor plan. Even better: do the whole thing in a 3D program. Model homes always only have minimal furniture. They have hardly any storage space. That makes even the smallest rooms seem big.

That's how we calculate as well.

Although you should definitely consider the individual case.
- Is an attic available as storage space?
- Maybe the garage will be planned a bit larger?
- Will a garden shed be planned?

Basically, you really shouldn't plan too tight. After all, you are putting a lot of money on the table. Usually the biggest purchase of your life.
If then the house really feels more cramped than an apartment, you haven't gained anything.

What can help:
Draw the existing/planned furniture into the planned floor plan.
Even better: do the whole thing in a 3D program.

Show homes always have only minimal furniture. They have hardly any storage space. That’s why even the smallest rooms seem large

On the other hand, you should also consider that the children will move out (our daughter is eight, we are building next year) and then the house might be too big. Another aspect is the size of the plot. If you only have 400 sqm, I would probably plan bigger as well, because there are few options for "storage rooms." We have 1,450 sqm and are building a 140 sqm bungalow with one child (second not planned) without a basement. We consider it the perfect size.

The question is also how priorities are set. We bought ~130 sqm in [the existing stock]. We have 3 bedrooms, 1 office, 1 living/dining room, kitchen, guest WC, and 1 bathroom. All rooms are really sufficiently large. However, space was saved in the kitchen, WC, and bathroom. The kitchen is a typical old-school kitchen, the WC only fits the toilet plus a sink, and the main bathroom is also small. If we take the office out halfway (since we have a cellar), 120 sqm can accommodate quite enough people. The attic is sensibly integrated as storage space and suddenly you have a nice little house. It just doesn’t fit the idea of many people who think the kitchen and bathroom each have to be 15-20 sqm.

The question is also how priorities are set. We bought about 130 sqm in existing property. We have 3 bedrooms, 1 office, 1 living/dining room, kitchen, guest WC, and 1 bathroom. All rooms are really sufficiently sized. However, space was saved in the kitchen, WC, and bathroom. The kitchen is a typical old-school kitchen, the WC only fits the toilet plus a sink, and the main bathroom is small. If we take the office out halfway (since we have a basement), 120 sqm can definitely accommodate enough people. The attic is sensibly integrated as storage space, and then you have a nice little house. It just doesn’t fit the idea of many people who think the kitchen and bathroom each have to be 15-20 sqm.

Well, you simply have a basement, that’s the difference

I claim that without a basement, with a utility room on the ground floor and 120-130 sqm, you won’t be happy long-term with 2 children... the attic as storage space doesn’t really help much. Usually, the only option left is to park the cars in front of the garage and use the garage as storage space. But I wonder if that is really the purpose of it.

You’re right about bathroom/kitchen being 15 sqm... That is indeed the expectation of many home builders today. But even if you don’t do that, in my opinion 120 sqm without a basement and, for example, 2 children will be very, very tight and difficult. In principle, all this is “not so bad,” for example if you rent, but if I had to think about paying off a mortgage for probably too small a house all my life, that would be very unsatisfactory for me in the long run... Just a thought on the side, one that you should definitely consider.

But yes, clearly everything has to be considered individually. The OP simply has to know what kind of person he is, what he values, what the future might bring, and what priorities he sets or wants to set currently and in the future.