Our slope location - ground slab vs residential basement

Nice floor plan, but not for your property

Where do you want the driveway?
How many rooms do you actually need?
Where should the garden access be or the main garden?
Basement/living basement/lower ground floor does not mean you can cheaply generate additional square meters.

I would plan the multipurpose room and building services in the lower ground floor with access to the main garden
Ground floor entrance, bedrooms, bathroom, possibly side garden access
Attic expansion reserve, storage room

Nice floor plan, but not for your property

I find your considerations understandable to minimize earthworks.

We are planning 2 full-height slope retainers (red in the picture) and then have a garden with 2 levels (see picture orange and blue).
Our three children will go to the attic and then we will have peace in the basement living area. We will meet on the ground floor and can get to the basement on the west side.

[*]3 children's rooms >12m2
[*]1 living/dining area 45-50m2
[*]Bedroom
[*]Office
[*]Possibly guest room
[*]2 bathrooms + 1 guest toilet

Your experiences also correspond with a rule of thumb we heard in a podcast.

How was the rule of thumb formulated there?

Nice floor plan, but not for your plot.

That's right, and ...

Our current building volume is 9.12m*8.5m.

... also does not match the sizes in the shown plan (?)

We are planning two room-high slope reinforcements (red in the picture).

That somehow sounds like the company Eulenspiegel & Schildbürger ...

How old are the children?
How do you want to bring garden tools, lawn mower, green waste from the garden to the street?
How do you want to connect the garden to the main living area?

I don't see the house with the budget?
Do you have offers for slope stabilization?
Does the [B'Plan] allow that?

How was the rule of thumb formulated there?

It can be found on YouTube at Hausbauhelden and is called "Keller oder Bodenplatte" ~ after about a minute this rule of thumb appears:
45m2 should preferably be added as a basement replacement area.

I don’t see the house with the budget?

The house is about 240,000 EUR without basement from a large Swabian prefabricated house provider.
The other house with 9.12m*8.5m is about 320,000 EUR with a livable basement from a solid house provider with a franchise system.

How do you want to connect the garden to the main living area?

There will be a door from the kitchen-living room on the west side. For that, the area must be filled up there and the slope secured.
That will probably cost a lot of money and we can’t quite estimate it yet. We haven’t spoken with the civil engineer yet and will only do so when we have a clear plan (with an architect).

The other house with 9.12m*8.5m is around 320TEUR with a living basement from a solid house provider with a franchise system.

What I think of them – in short: keep your distance – you should have read here occasionally.

The house is around 240 T EUR without a basement from a large Swabian prefabricated house provider.

The timber frame panel builders are usually not the first choice if you want or should build a living basement. This applies especially if the house manufacturer has no established cooperation with a basement builder. Then he sees the equipment of the basement with living spaces somewhat as a competitor for the part of the budget he earns from (and tends to argue the living spaces above the upper edge of the basement ceiling).