Pay attention to small details in planning: towel radiator, etc.

Super... I have already gotten a few ideas. The second outdoor water tap and the central switch for the roller shutters are noted, as well as the empty conduits for the air conditioning.

What about these rimless toilets? Is it really worth it?
Alarm system sensible? What are the opinions of those who have one?

By small things, I meant items that generally cost around three or at most low four figures. A double garage with a tool room and roof terrace is, in my view, not a small matter but quite a significant change.

We have rimless toilets, I would take one if you like one. Another tip: switch for the light at the mirror also next to the door or something like that.
Empty conduits from the roof to the basement for photovoltaic are also installed in our house.
In the kitchen maybe as a tip: deep countertops/surfaces at the walls – we have 75 cm and additionally extra deep drawers with 70 cm usable depth.
Underfloor heating in the basement (hallway UG) is also great, turn it on there and the whole staircase including hallways on the ground floor and upper floor are warm.

Yes, when it comes specifically to small details: I have the impression with many front doors that the lock cylinder would have liked to be installed about a centimeter further away from the frame. This usually only turns the mortise lock into a "custom size" and costs only a little more.

What I also find practical and inexpensive are fixed glazing panels under the tilt-and-turn sashes at some windows, as high as potted plants.

Overdeep countertops are really very practical
if the house can be big enough, I would always plan to put the washing machine where the laundry is generated, usually the upper floor

if the house can be big enough, I would always plan the washing machine where the laundry is generated, usually the upper floor

I prefer the laundry chute there - also such a useful little thing. Although I would design it as a multi-chamber chute so that the types of laundry can be sorted already "at the source."

So rimless toilets I personally find great (hygiene), but if it doesn't fit the budget in the end and you otherwise have to make compromises on other things (which are not so easy to change later), then I would initially do without them. They can also be retrofitted later without too much effort!