Single-family house with double garage, approx. 190 sqm ll Improvement suggestions

By the way, the good gentleman forgot the chimney draft on the upper floor.

Basically consistent. I would possibly build a second bathroom on the upper floor, specifically where the hallway is quite large. If there are four of you and both children go to school, it can get tight if four people want to use the bathroom at the same time. Also, the guest bathroom would then be tidier and you could omit the shower there.

If a full basement is to be added, the 500,000 budget will likely be very tight. I would build the fireplace as a masonry stove, otherwise the corner will quickly overheat.

We paid 540,000 € for our house (170 sqm, partial basement, double garage, and fireplace), and that was already three years ago.

Also, budget enough money for the outdoor facilities considering the size of the plot. The garden is certainly not small.

Why not the driveway to the garage from the street? Then there is a nice west-facing garden.

At first glance, I like it. Very nice ground floor (if you place the access door to the open space aligned with the staircase axis).
I don't like the upper floor – I would adjust it a bit. However, the design is not clear to me in relation to the plot and orientation.
And somehow, without reading glasses, I can't make sense of the plot/site plan. Where exactly do the 1000 sqm end?
By the way, the good gentleman forgot the chimney flue on the upper floor.

The shower in the bathroom under the sloping roof, does that work?
You can also fit the linear meters of wardrobe into the bedroom without a dressing wall and gain a space for yoga in front of the wardrobe

I am especially curious why you are allowed to build in the outdoor area. :)