Single-family house 175 sqm without basement, too big?

It was not about the house from Hampshire,

I already thought so ...

but about the implementation 2 adults + 2 kids who are almost grown up

... and exactly for "a guest house for the boys" you need a property that plays along. A slope and forest are not necessary, but the size is certainly noticeably helpful.

It is also possible to build a small apartment in the city villa, as proposed and rejected here.

One can also build a small apartment in the city villa, as suggested and rejected here.

Yes. Definitely a granny flat for 2 KfW payments!

No, seriously, I don't think much of that and everything should be considered individually. The entrance is supposed to be in a wind tunnel? I wouldn't do that,

I moved out of my parents' house at 19, my partner at 18. I myself grew up in a multigenerational house and did not experience it positively. I find it legitimate and understandable if other people plan it that way, but I am not planning to spend a lot of money on an apartment that I don’t know if it will be used and even if it is, for how long it will be used.

I doubt that has any effect. The room is simply heated through the other rooms anyway; it's a thermal envelope overall.

It definitely has an effect. You can test it in winter: heater off and door closed in a room.

Hello
I have spent some time working on the window planning. Attached are pictures with the measurements of the windows (width x height).
Do you have any opinions on this? Overly large? Way too small?
On the upper floor, I chose the version with a fixed bottom part for the floor-to-ceiling windows because French balconies are very expensive. Is that okay? Oh God, how ugly?
Please share your opinions!