Single-family house with 3 children's rooms

Because of the width of 19m, there would still be about 5m of garden at the bay window. The current variant is the best possible compromise we could think of. We have also balanced it out somewhat with many windows facing the "main garden," so that you can look there from many places in the house. But unfortunately, we couldn't come up with anything better, as the building envelope is quite limited.

Yes, of course that's thin, but it's also not your job.

But of course, we would be very happy about your creative ideas.

Haha, that's like a free pass to cover everything with paving. The spirits I summoned...
...will come as soon as there is time.

What is the dressing room in the basement: storage for seasonal clothes or shoe cabinet?

Am I correct in assuming that the development plan-required roof terrace means owing a unnecessary balcony in the attic to an enlarged ground floor solely to avoid a full storey?

By the way, here is a "comparison thread" of another maneuver-prone neighbour:

If you ban your guest to the basement and have the utility room there, so already have water connections, I would also grant the guest a small bathroom.

If a lifting system is required, there should technically and price-wise be a noticeable difference whether greywater or blackwater has to be lifted.

Nice design - and if you ask the building authority politely, there might be a chance to push the house further into the plot. Talking can help.

I would skip the shower on the ground floor - in old age there is a stairlift anyway. If that’s not enough, it’s too tight downstairs anyway. Instead, consider having a bathroom in the basement. Maybe a sauna will be added someday.

Whether the "maneuvering" in daily practice is annoying or not is something only you can decide. Every time we come from the main direction, we have to perform a turning maneuver to get into our driveway, which runs almost parallel to the street. It’s just like that and doesn’t annoy us.

The terrace around the corner will surely work great.

Go for it!

Am I right in assuming that the development plan-related roof terrace means that an unnecessary balcony in the attic is simply due to a ground floor enlarged to avoid a full storey?

Yes, that is the plan.

The dressing room in the basement is rather for seasonal items and clothes/handbags/shoes etc. that are rarely worn.
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Regarding the building line. I don’t know the exact technical difference. But for us, the development plan precisely specifies where on the plot this 11x14m area may be built. This is at the location described above, with the option (by exemption application) to possibly shift the entire building envelope 3m to the rear.

No, a building line means that the edge of the house must be exactly at this line. In contrast, without a building line, you are allowed to freely move your house within the building boundaries.

Whatever kind of line this is, there are no rules without exceptions. So go to the building authority with a plan and kindly present the concept and ideas to them – then maybe something is possible. We have had very good experiences with that.