Comments on floor plan design welcome

We would like to plan so that today we already have everything we need for daily necessities on one level.

And yes, I can handle a lot of fuss and I respond accordingly. Don’t worry.

That makes sense, we don’t follow it entirely consistently because of the quoted sea view as well as the optional way to install a stairlift.
Personally, I wouldn’t plan a separate room on the upper floor for each usage, but I would have pipes/connections installed in the wall already to later be able to have a separate apartment. I think one room can be both a guest room as well as an office, hobby or TV room, one would be enough for me, and I wouldn’t need two extra rooms for the children who come sometimes. I usually try to think according to the principle: What is frequent – and what is rare, and from that the decision mostly/ not always results. Keeping rooms in reserve does not make sense to me because it would take away space for my own life; I like living generously. Wife downstairs visiting – me upstairs watching TV, wife annoyed by me – upstairs in the hobby room or me in the garden house –
We think the same way, but we are also not entirely consistent there; such an apartment could easily be accessible via an outside staircase for us, so possible. Or... who knows, you yourself move upstairs and the child or whoever else separately downstairs.
So I’m already imagining how a separated living situation could be without disturbing each other; nevertheless, everything will be subordinate to my current life as I like it today.
Should the case arise that the upper floor apartment is needed, it must be so that you can complete the separation with only a few measures and create an entirely separate apartment on the upper floor, including kitchen connection, sewage, TV, telephone, stairs, separate heating room, separate water meters, electricity meters etc. This is not free but still implementable beforehand with manageable costs.

… I never doubted that either and I myself am storm-tested –

and now imagine you would have a floor plan evaluated here with such a post... first question: what do you actually want. second: first get clear about your requirements. third as a statement: anyone who is still so unclear about their life situation should not even build.

NO - and that is now -again- your incorrect conclusion-
NOW it is -again- clear that it will NOT be a two-family house but a house for two who want to live on one floor, sometimes have visitors, and partly plan ahead for their own old age; optionally 1-2 rooms and a shower/toilet on the upper floor, which could possibly even be separated.
If you stick with that now, it is no longer quite so difficult-

which budget do you have for the construction including ancillary building costs?