Floor plan design of a semi-detached house for 1 family (4 persons) on a small plot

you are wasting an essentially priceless opportunity.

Most advice is of little help

Well, what can one say?
I thought about whether to respond at all. I too do not agree with people who do not take care of their affairs.
Nevertheless, there was probably one "planner not suitable" sentence too many, ultimately this inadequate self-design, so I replied. I could have also rested after a tiring day. But that is my business, how I plan my free time.

There may be a little stubbornness in you – but that won't get you any further.
Advice must first be allowed to take effect. It can hardly be received yet, especially when one is somewhat disappointed oneself.
But of course there are also such people who do not want to be helped, even if they post anonymously in a forum.
What was your statement?

therefore I hope to benefit from the collective knowledge and experiences here in the forum.

So be it. Ultimately, you are responsible for what you make of the suggestions.

You don't have to reinvent the wheel for such simple basics. The tricky parts are at most the parking spaces and the budget.

Tricky are at most the parking spaces and the budget.

The parking spaces are solved by also using the "front" building envelope for them. And the budget by being honest about how much (or how little) of the cellar desire is dictated by the property; then you can be advised here by the egomaniac-scolded helpers. A non-mandatory cellar is definitely more expensive than all postponable attic expansion cost items combined. And a necessary cellar can be utilized in such a way that upstairs there is maximum available house depth space for the parking spots.

You don’t have to reinvent the wheel with such simple basics.

It’s actually better not to even try that. If the potential for floor plan variations here were worthwhile hunting grounds, the models of the usual suspects wouldn’t resemble each other so extremely strongly. By the way, they regularly have an optional master bathroom in the upstairs storage room.

If the potential for floor plan variations were lucrative hunting grounds here, the models of the usual suspects would not resemble each other so extremely strongly.

P.S.: and entire departments are paid for that to make the floor plans more perfect and more attractive for customers than those of competitors. The customers, namely - beware arrogance of an egomaniac know-it-all! - hardly look at the share capital and other insolvency-relevant financial figures of the companies, but are totally fixated on the floor plans. By the way, when buying a car, people also don't ask if they can buy the back seat later and feel misunderstood by product developers for not offering the Golf with Focus engines.