Is financing a single-family house feasible for us?

Party room? How often is it used, once a year? You could also use the living room for that. Woman's idea?

Of course But currently we celebrate at least once a month in the parents' double garage

Am I the only one who would NOT paint the basement on a 300m² plot because there is simply too little space above ground for a basement replacement room? How is the big house plus double garage supposed to fit on the plot at all?

We don’t have a significant garden except for the required clearance areas to the neighbors. Several neighbors built without a basement, so of course it’s possible. But we would simply prefer a basement. It can’t be added later and you might end up very annoyed. Eventually, we will both inherit our parents’ houses, and at the latest then you can still build a garage, but not a basement anymore. But considering what everyone else around us is building, it must surely be quite tight for several of them. I can’t explain how it works for all the others.

Of course. But currently, we at least celebrate once a month in the parents’ double garage.

We don’t have a significant garden except for the required distance areas to the neighbors.

Several neighbors have built without a basement, so of course it’s possible. But we would simply prefer to have a basement. You can’t add one later, and you might get really annoyed.
Eventually, we will both inherit our parents’ houses, and at the latest then you can still build a garage, but not a basement.
But with what everyone else around us is building, it must be quite tight for several people. I really can’t explain how it works for everyone else.

Also consider individually. We would really be the very last to give up the basement and will also build with a basement. Nowadays, many actually build without a basement. But I also think this is because the advantages of a basement are not recognized since it wasn’t present in their parents’ house. Anyone coming from a house with a basement knows exactly that with 140-150m² it could be difficult without a basement, or that many things are handled differently nowadays and people don’t see the many advantages—which I consider very, very important—as advantages at all. But as I said, always consider individually. You have to decide that for yourselves. A basement is very, very expensive, but to us it is worth every cent! I would immediately give up the garage if I had to!

Of course But currently we at least celebrate once a month in the parents' double garage

We don't have a significant garden except for the required distance areas to the neighbors.

Several neighbors built without a basement, so of course it's possible. But we would simply prefer to have a basement. You can't add one later and you might get really annoyed.
Eventually, we will both inherit our parents' houses and at the latest then you can still build a garage, but not a basement.
But with what everyone else around us is building, it must be quite tight for several of them. I really can't explain how it works for everyone else.

I also can't imagine how to build on 300 sqm, but that's another topic. We are planning with 140 sqm and 1x bedroom (14 sqm) + walk-in closet (5.5 sqm), office (13.5 sqm), children's room (15.5 sqm), living room (28.5 sqm), kitchen + pantry (15 sqm), utility room (9 sqm), bathroom (9 sqm) + guest WC (2.5 sqm). With 160 sqm you could theoretically add a large room. So why still a basement?

Also consider individually. We would really give up the basement as the very last option and will also build with a basement. Nowadays, many actually build without a basement. But I also think it stems from the fact that the advantages of a basement are not recognized because one did not have it in their parents' house. Anyone coming from a house with a basement knows exactly that with 140-150m² without a basement it could be difficult. But as I said, always consider everything individually. You have to know that for yourselves. A basement is very, very expensive, but to us, it is worth every cent! I would immediately give up the garage if I had to for it!

It also depends on the size of the plot. Ours is 1,450 sqm, so you have other options to create storage space.

It also depends on the size of the property. Ours is 1,450 sqm, so you have different options to create storage space.

Exactly, also a topic! With an "alleged" 300m², a basement can already be very useful.

Although this is also a topic of: storage space inside the house or outside the living area. I am certainly in the lower third with my opinion, but as already said, always to be considered individually. According to the OP, however, everything sounds to me as if the basement is indispensable, which in my opinion is not bad at all and I totally understand.

@OP: I understand you with party cellar or hobby room etc.

Additionally, with a basement, everything basically looks tidier as there is more space available. I wouldn't feel like throwing everything into the attic, parking the other half in the garage and thus parking my car in the yard, as it currently looks with almost every new build.
Besides, then the few small "storage rooms" you have are not really tidy and offer little space.
Then the topic of laundry... For me also a very decisive criterion, which for many apparently isn't a problem at all.

But with what everyone else around us is building, it must be quite tight for several people. I really can't explain how it works for everyone else.

It definitely is. Of course, no one will admit that. There are probably all kinds of scenarios like a lot of equity saved up like you, inherited a lot of money, or simply very well-paid jobs.

By the way, the topic of celebrating once a month is off the table as soon as you and your friends have children. Sure, one day it will happen again. But until it happens that regularly again (if at all), it will most likely take many years.