Land planning - which house type/size is most sensible?

Yes, that's correct. The architect first makes a cost estimate. Architect or general contractor, you can see it either way. A general contractor is not just any general contractor, and an architect is not just any architect. With a general contractor, you should be able to work with the construction method they are familiar with... breaking out of their known system is usually not advisable or sometimes associated with significant additional costs... with an architect, you are more flexible. But making a pro-con list here would, I think, be off-topic and too extensive. Stay with it, as a basis I would think of a rectangle. Approximately in a 3:2 ratio and carport to the northeast. Two full floors or at least knee wall in the direction of 2m or above.

Stick to it, I would think of a rectangle as a basis. With a ratio of about 3:2 and the carport facing northeast.
Two full floors or at least knee walls around 2m or above.

My favorite is also a rectangle with at least knee walls from 2m.

How can I, as a layperson, recognize where the building boundary is or whether boundary construction adjoining the neighbor is allowed?

One general contractor, for example, recommended that we consider this house. A city villa.

That would be a square

I hope not in orientation then.

Building boundary...the dashed line in the development plan.
Boundary construction for the carport. It varies regionally...state building regulations, local building ordinance, textual determination or justification....but you are not building anyway

That would be a square

I hope not in that orientation.

Building limit...the dashed line in the development plan.
Boundary construction for the carport. This varies regionally...state building code, local building regulations, textual stipulations or justification....but you are not building anyway

Square, husband's ideal vision.
External dimensions 10.115 x 10.115. that was also the house he liked in the catalog.

However, floor plan somewhat different.

How would you orient this house? So I can get an idea of it

If you want to join the floor plan discussion, it would be sensible to fill out the questionnaire. For me, the floor plan is awful, for you and your requirements it might fit and be considered good. Just as a hint. By the way, one can ask oneself why a 17-meter-deep plot is being built on with a 10-meter-large house. I would keep the hedge in the north.

Just request catalogs from the major home manufacturers and browse their websites.