First floor plan available, what is the exact procedure for construction planning?

Flat roof, no basement, two children...

Where do you plan to have the necessary storage space?

We would like to change something (generally make it a bit smaller

This is usually difficult to impossible. Often the furniture drawn in these floor plans is a bit small. If you seriously look at how much space you need or consider reasonable (dining table set as an example), you will often realize that another 20 cm would need to be added. And then you often also forget built-in walls and similar. What I want to say with this: Think about which functions/rooms you need. Write that down. Then look at which floor plans from catalogs fit without changes and/or go to an architect.

With your own plot, especially such a beautiful large one, I would definitely go to an architect.

We would like to build with a regional construction company. Acquaintances built with this one and reported €1200 / sqm as a rough benchmark. Since there are of course extra wishes (large washbasin, walk-in shower, ventilation system, fireplace, multiple sockets, electric shutters...) we of course expect higher costs.

As others already said: That probably won't work.

3. Possibly we would only request the slab for the garage and the so-called HAR and later build a garage on top ourselves - can you give me approximate costs for a project to build/have built a garage with a footprint of 55 sqm?

We have a garage exterior dimensions 6.50 x 9 m.

Cost including excavation and disposal, slab, waterproof subroof, gable roof with clay tiles, exposed screed with broadcast, colored exterior plaster, interior plaster, electric 5-meter gate 2.25 high, 2 windows, side door and electrics almost exactly €30,000

We have a garage with external dimensions 6.50 x 9 m. Cost including excavation and disposal, base slab, waterproof underroof, gable roof with clay tiles, exposed screed with scatter, colored exterior plaster, interior plaster, electric 5-meter gate 2.25 high, 2 windows, side door and electrics almost exactly 30 kEUR

We have almost the same dimensions and equipment, but as a detached garage and fully bricked: ~47kEUR.