Support hanging and filling - Additional costs?

Without knowing the elevation points and alignment, I would plan it similarly to how we do.

The top edge of the floor slab is 1.2 m above street level for us.
Ground floor or basement, whatever you want to call it.
Utility room, wardrobe, entrance, common room, guest WC, garden access
Upper floor bedroom 2 children's rooms bathroom laundry
Attic not developed
No idea how many have wanted to offer us a basement or an underground garage. For what? Give up garden access? More stairs every day?

Just post your site plan with contour lines. Black out the street

I somehow can't really imagine it.
So you basically built a basement and use it as living space and then put a house on top? Or how should that be understood?

I added a picture. Hopefully it is recognizable.

Base slab WU retaining wall solid wood remainder

With us, a large part of the earthworks was already completed due to the old development.
And south is on the valley side for us.

When I look at your site plan
- without knowing the development plan -
Garage and house technology, entrance and 2 rooms in the basement (when the children are older maybe the parents' area nice and cool)
Ground floor open plan and garden southeast
Attic the rest

Or carport separately in the west
Below entrance, technology, bedrooms
Above open plan and office possibly even with open roof structure

You have to see what the development plan allows.
You have to plan so that as little excavation as possible is required and not more enclosed space than necessary.

Every cubic meter costs.

A basement can be full-fledged living space. With higher ceilings, bright and friendly.

Ah, now I can imagine it much better. Great tip!

What is a WU back wall? And how do you "order" that from the provider?
Did you build a solid house or a prefabricated house?

Our regulations unfortunately allow only 1.5 stories, but a basement may be an additional full story.

WU concrete is waterproof concrete. Used for white tanks.

You are looking for a partner (architect, general contractor) who builds your house according to your wishes. Whoever doesn't do that is out. The whole thing grows. One step at a time. It overwhelms you at the beginning. The general contractor doesn't sell you a house that doesn't hold the slope. The static calculations and the soil survey flow into it. That will be. You must never lose sight of your framework and wishes. Deal with your [B‘Plan]. Articulate your wishes as precisely as possible. Not just laying down a floor plan, but dining table for 12 people, dressing room with 6 linear meters of closet, wardrobe must accommodate the shoe collection, living room with XXL sofa 7 m ceiling height shelves for books, gallery absolutely not, etc.

Look at show houses and catalogs. Present pictures of what you like.

We're doing it roughly the same way right now. It's just very, very difficult to decide and weigh who ultimately makes good offers.

PS. What is a GU?

GU is a general contractor