Unequal width in the planned semi-detached house

At the top left is a part of the recess for the cistern, which is 6x6 m in total.

Does that mean? Can the driveway be planned there?

Living area would certainly not be 150 m, but rather around 135 with walls and staircases.

No, rather over 155. I have drawn it. However, I calculate the gross floor area and certainly do not deduct areas under the stairs like in residential construction. That distorts a calculation.

550k would be approximately our pain threshold.

Only the house or including ancillary building costs and outdoor facilities?

Cost estimate of about 530k for the project including basement

Yes, you would have to know the construction performance specification. If it is a standard construction performance specification, I would add another 40,000-50,000 to the estimate above for earthworks, removal, and special equipment.

I honestly don’t find this post helpful at all... The plot is flat, so no hillside. The basement is simply important to us, and we’re trying to find sensible options for it. The current plan is either a) discuss with the other party that they "pull down" a wall as part of their earthworks up to the end of our basement or b) quickly agree with a contractor and planner and at least build the basement before the slab.

a) is – as I have already implied – a fool’s errand, b) would be my first choice for a plan B (plan A, as said, is not to build a basement against the plot vote). Was that "helpful" enough now?

Personally, I would always want to avoid a basement. It only generates storage space after all.

This is the common misconception here.
A basement can be much more than storage space.
If you raise it one meter out of the ground, you can give it wonderful windows and thus have fully usable rooms. Without expensive and vulnerable skylights and without annoying sloping ceilings.
Space for a utility room, technical room, office, workshop for people who want to do something all year round, hobby room, and even children's rooms.

Pulled one meter out of the ground, you can give it wonderful windows

Exactly! I wrote here:

And also in the basement, you could create living space if it is built to be suitable as a living area. There are also basements that are larger in floor area than the ground floor, where you can then plan a skylight at ground level. Or conventionally, a light well for a larger window.

Actually, as an opponent of underground floors, I still wanted to advocate for it,

This is about a specific construction project. And so on, we do not need to go around in circles and misuse individual passages from a post.

This is about a specific construction project. And so on, we don't need to go around in circles and misuse individual passages from a post.

Yes, and exactly in this construction project you then say that it would only generate storage space. Although the OP clearly says that the basement is non-negotiable because he wants the space.

Yes, and exactly with this construction project you then say that it would only create storage space.

No, please differentiate statements where personal opinions are made in general (the quote from me that you used) from the direct advice regarding this construction project.