Floor plan design for a single-family house - opinions and tips?!

Yes, it is hardly worth listing all the problems individually. It simply has to be started from scratch. But for the unbelievers here, just a few serious ones:
- The huge basement resembles a nuclear bunker. What do you want to do with it? Are you moles?
- The staircase takes up the space where you would expect access to the terrace / garden.
- Kitchen / dining area too small, but tons of storage rooms.
- Office and guest room are a joke - actually just more storage rooms again.
- Office is not needed at all - probably the corner was leftover.
- Two staircases to the basement - that’s one way to sink your money.
- Toilet + mini bathroom in the basement definitely requires a lifting system - who wants that?
- Placement of the house on the property still somewhat unclear. Where is the terrace supposed to be?
- etc.

I am still drawing the Budget card
Large garage
XXL basement
2 staircases
2 bathrooms, 2 toilets
Water-circulated fireplace

The plan contains an imbalance of rooms
For example, the hallway on the ground floor is larger than the storage room and study combined

The study and guest room just look like leftovers.

Kaho and Kbt09 have also listed some points that should be changed.

... plus basement garage... Why do you need so much storage space? That's even more than the actual living area. said it all with her two-liner. Even such honest hard truths must be swallowed by a questioner when things are as they are. That greatly shortens the misstep in planning.

Now that's what I call a meaningful contribution...

Where exactly is a constructive message hidden in your post?

Some basic ideas (which are in the floor plans) can already be used. However, what is presented now is not ideal. The basement under the garage costs you a lot of money: Why do you need such a huge cellar? I also don’t see how you can manage all this with 450,000 euros. The layout and the contents of the cellar can only be discussed once you know exactly what you want on each floor: Is there a "requirement list" of rooms per floor? Then I would start with that (including room size). Only when this list exists can you work on the floor plan. Otherwise, it remains a makeshift job that is not necessarily effective. It is therefore not entirely clear why there is no WC with a shower on the ground floor (and instead none in the cellar). I suspect that we do not have all the information that led to this floor plan. The third children's room on the upper floor is really too small to count as such. A lot of space is lost to corridors on the ground floor. The size of the kitchen/dining/living area is very tight considering the lost hallway space. Try marking out the same size in your home: then you will immediately see if it is really sufficient for your needs. Is the driveway to the garage from the northwest? A north arrow on the floor plan would be helpful. Conclusion: put the floor plans aside, start anew with the room requirements per floor. Possibly incorporate one or two ideas from the floor plan when redoing it.

Overall, I am not a big fan of this design either. Are two small workrooms on the ground floor and the attic really necessary? The basemented, insulated garage is, in my eyes, excessive luxury - a cost driver. This room concept also requires three burglar-proof doors at once. The kitchenette would have to be L-shaped along the wall, so that you don’t have to eat with only four people for the next 20 years.