Avoid mistakes in the second house: Home construction company or architect?

Feel free to do that, I would be happy about it,

Yes, then turn your Would-like-could-be-happy into concrete action and leave a corresponding comment where you found the flat threshold post (and also find "The upper floor takes priority") at "You have the choice: the next consultation offers" ! - "interactive" also means: if the couch potatoes remain passive, there will be no new chip bags.

because drawing floor plans is still difficult for me. "More systematic than artistic": Do you mean, for example, first drawing all the rooms you need on cut-out cards and then rotating and arranging them until everything fits?

You have already caught the scent of the right direction, but you still turn into the dead end of the "supposed final straight" too early. You also have that when you drive south on the cathedral side to me: half a kilometer before the correct exit there is a (often littered) rest area. Before drawing, first write lists. In the second step, the list of rooms becomes a table: approximate room sizes are added. Then the rooms are assigned to the levels (equal axial load for the Anstattvilla, unequal axial load for the one-and-a-half-storey house; note three-quarter or two-thirds federal states !). Only then do you start with the drawing "layout," preferably using the card method, with the more complex storey ...

I usually start drawing with the kitchen/living area and then somehow can’t manage to sensibly add the remaining rooms.

... so definitely not with those first, since they are usually located on the derived storey!

You write your musts down like 2nd refrigerator

... which is planned rather not to be in the hallway.

Consider when planning the rooms whether every child really needs a room, my first thought would be 4 children, 2 children's rooms of about 15m2. I know many children who anyway huddle together and want a sleeping room.

Consider in room planning whether every child really needs a separate room, my first thought would be, 4 children, 2 children's rooms of about 15m2. I know many children who cram together anyway and want a shared sleeping area.

They currently sleep in one room and like it very much, but they are still very young. When they start school or at the latest at puberty, each should have a private retreat. So we still have time, but we are already thinking about it.

Also keep in mind that the children will move out eventually, so that you don’t start planning the next house for old age just two years after the upcoming one. The many square meters needed to be maintained both in terms of cleaning and energy efficiency.

Consider when planning the rooms whether every child really needs their own room,

They now sleep in one room and really like it, but they are still very young. When they are in school or at the latest during puberty, each should have a retreat space.

Also keep in mind that the children will move out eventually,

Children are quite dynamic roommates, whose needs profile almost requires rooms as flexible as the Barbapapa family. Four rooms for four children is okay but rather not in a static assignment. Perhaps one of them as the "room of the best-behaved child of the month," bedroom, living room, playroom, oldies stay-outside room.
Let go of all "hopes," that would be four constant rooms.