City villa floor plan 180m², basement, 3 children - Your opinions on this?

But that's not a price estimate with basement, is it?

Where does the street run? Are trees being cut down there?

Can you provide some dimensions? I know the program, and to my knowledge this standard staircase (or any other staircases) of this program is not worth mentioning, but have to be adjusted in size.
4 bedrooms in 10 x 10 is not exactly what creates optimal rooms. Trying to fit 3 equivalent rooms in 9.20 is not feasible (as you can see). How wide is the bottom plan? 2.60? 2.45? On top of that, a living sqm (the one at the door) is lost.
How wide is the bathroom? 1.60? How long is it in total? 7 meters? What do you do when 3 people are in there? Traffic light control? That was a joke, but honestly: with the necessary pre-wall installations, not even the bathtub is justified where it is.
How wide is the pantry? One meter? Where should a freezer about 60cm deep be placed, and how should the other walls be designed then?
I find the floor plan anything but final or anything like that – it is a draft, from which you can tell that 3 rooms only moderately fit in 10 x 10. The next step would now be to say goodbye to 10 x 10.
I also consider the budget to be too tight with a living basement or heated basement. https://www.hausbau-forum.de/attachments/grundrissplanung-unbedingt-vor-beitrag-erstellung-lesen-79977-1-jpg.10450/
Minimum dimensions of stairs...

The floor plan is good, only the pantry I would reconsider. Try furnishing it. More than a narrow shelf will not fit in. You do have a basement: so get rid of the pantry, enlarge the kitchen and add more windows on this side (For example, a high strip window can also look great in the kitchen).

Office: Family use or home office?: Only home office. Before corona at least 2-3 days working from home, in 2020 a total of 10 months working from home, after corona probably at least 3-4 days home office

Where is the study or desk corner?

Apart from the bathroom, I like the floor plan. Unfortunately, I cannot "read" the plot, would the basement be partially above ground? However, the budget for 180 sqm plus basement seems very tight to me?

Plot size is 880 sqm, is that enough? We were advised against a ring trench collector, although the plot is big enough, it would be too ineffective.

The plot is more than enough! And there are hardly more efficient systems than a ring trench collector. But no plumber has experience with it since it’s not really widespread and those who have it often do it themselves. So you definitely have to get informed, there is a forum for it. There are a few conditions that can probably be well met here. Have the heat demand calculated (general contractor/construction manager/energy consultant?) There is also a suitable tool linked there (Trenchplanner) with which you can calculate the ring trench collector yourself after some practice. Rent an excavator and do most of it yourself before the start of construction (if possible). Of course, find a plumber beforehand who connects the ring trench collector to the heat pump. For comparison: Our 220m borehole (2x110m) should cost about 12K. The ring trench collector with own labor is certainly less than half, even with a rented excavator (about 40€/h) + driver. Unfortunately, I only realized that "too late," so there remain some gaps in the planning. It’s impossible to plan everything perfectly yourself because you simply lack the knowledge. That’s why it’s definitely worth handing over a few things to trusted :cool: craftsmen.

Price estimate according to architect/planner: 400,000 without ancillary construction costs
Personal price limit for the house, incl. fittings: 415,000

What does incl. fittings mean? Painting, flooring, kitchen?