Floor plan 161m² - Have we missed something?

The building plot has no development plan, construction must be according to §34 Building Code. According to the municipality and the building environment, "almost everything is possible"
[...] Number of parking spaces: none as there is no development plan!
Number of floors: none as there is no development plan!

Vegetable garden, greenhouse: Yes, gladly hobby gardeners ;-) (he)

Regarding saving money: If the house is really "almost a passive house," get rid of the stove/fireplace and the chimney.

I just skimmed through it...

You estimate just under 600k but only want to spend 500k? Office with 16 sqm, a pantry, a walk-in closet, an entrance hall with 16 (14) sqm on the ground floor and a corridor with 10 sqm on the upper floor.
Efficiency definitely needs to be optimized here. Can you transform the strongly rectangular floor plan more into a square one? That way, several square meters of the corridors can be added to the rooms, the office can be reduced somewhat, and the room sizes and accesses on the upper floor can be optimized. With the current floor plan, there is hardly any possibility to place a wardrobe or similar at the entrance.
I also did not see a budget for a kitchen, did I possibly overlook that? (587,000 - 530,000€) 57,000€ for kitchen, fittings, flooring, and finishing walls might be tight.

I agree with the previous posts, there is almost always room to trim and combine things. For example, a large utility room downstairs, which also leads to the side entrance door and houses the washing machine/dryer. Possibly something from the pantry could also be integrated there, saving overall square meters on the ground floor and potentially making the kitchen bigger. The storage room upstairs could then be omitted, the rooms made a bit narrower, and that way savings could be made on both levels. But there are plenty of professionals here who can think such things through properly and even draw them up, so surely much more helpful input will come.

What also caught my attention: the walk-in closet seems pretty pointless to me. Only about 2.5-3 meters of wardrobe fits in there?! The rest are walking paths where you could at most fit a chair (for the not-quite-clean-not-quite-dirty clothes) and a small laundry collector. The visual separation doesn’t bring any practical advantages if the partner is bustling around right behind the headboard early in the morning. I would reconsider whether this really is the best option for a actually quite large bedroom.

From my point of view as well. But…

Isn't that contradictory? Planning for 2 people and a children's room?

Or are some planned?

And what do you want to save on? The mentioned windows?

Regarding the floor plan: I don't find the open living area successful at all: 3.60 meters is quite narrow for a living room. With the length, the room becomes a corridor. The children's rooms are also corridors.
Bathroom with 2.80 meters will be very tight and only feasible with a small tub. Bedroom as a walkthrough room is not advantageous.
There is also no adequate access to the garden, only to the south terrace, and space there is limited and the boundary is close.
I would plan the open living area in an L shape in the southeast, which would benefit a lot. Also the entrance in the north. Move the garage to the back, i.e., shift it to the right side of the plan. The rest will follow.