ᐅ We are planning to build a house. Is what has been offered to us acceptable?

Hello, we would like to start building our own home this year with a general contractor, a complete package.
Since I am not very knowledgeable about this topic despite a lot of research and cannot properly assess such matters, I wanted to ask what you think about the offer we have received. We are currently strongly leaning towards this provider.
We are curious whether this is more or less "standard" or if it is rather on the lower end. Also, what could possibly be improved without immediately having to pay several thousand more.

First of all, many items are listed as “insulated,” such as the lowered ceiling in the bay window, the roller shutter boxes, or the solid knee wall.

Floor:
Reinforced concrete slab foundation including frost protection edge strip and waterproofing against rising damp instead of strip footings. Thickness about 20cm (8 inches) and concrete quality C 20/25.
Steel reinforcement and slab thickness according to the assumed ground pressure as per the homeowner’s specification sheet (I can provide that if needed). A foil is laid under the slab as a clean layer.

Walls:
The exterior walls are executed with a total thickness of about 44.5cm (17.5 inches) as follows:
1.5cm (0.6 inches) fine plaster
17.5cm (7 inches) masonry of porous, fired clay brick
14cm (5.5 inches) cavity insulation, thermal conductivity class (WLG) 035
approx. 11.5cm (4.5 inches) facing brickwork
Interior walls on ground and attic floors are constructed with brick (Poroton).

(Now the addition for KfW 70)

The piping for the warm water underfloor heating is designed for a supply temperature of 35°C (95°F) by installing the pipes closer together.

Extension of roof insulation to 26cm (10 inches) with WLG 035
(Credit of 4,216,- if omitted)
[Is that reasonable for slightly better insulation and closer pipe spacing?]

For an upgrade to KfW 55 (20k-21k):
Different heating system with more solar input.
Ventilation system.
8cm (3 inches) insulation with WLG 035 under the slab.
Exterior walls then apparently no longer face brick but rendered, consisting of:
1.5cm (0.6 inches) fine plaster
17.5cm (7 inches) masonry of porous, fired clay brick
20cm (8 inches) external thermal insulation composite system (ETICS) with WLG 032 including silicate facade plaster.

Now my question is: since I would like a ventilation system, should I improve the insulation somehow even if I do not aim for KfW 55? And isn’t the masonry thickness of 17.5cm (7 inches) rather thin?
I skimmed a forum where this exact wall build-up (by the same contractor) was heavily criticized.

Are you building with a basement? There is no perimeter insulation listed for that.
Wall insulation looks fine.
You should get an explanation of what "closely spaced" pipes/conduits mean and what that implies.
26 cm is quite substantial—but why not? (It’s closer to a KfW 40 standard if you look at it purely from an insulation perspective.)
You could also just add 2 cm more mineral wool insulation to the wall... but that’s fine.
The wall construction is good—if it’s structurally sound. If you aim for KfW 55, tell the contractor to add 2 cm more mineral wool insulation. What kind of bricks are those? What is their thermal conductivity?
I would recommend installing a ventilation system—even in our apartment from the 1990s, occasional airing gets annoying.
You could add the 8 cm of insulation under the slab.
What kind of windows will be installed? What are the Ug and Uf values?

No, we are building without a basement.
So, the exact type of bricks to be used is not specified. Unfortunately, there is no information about the thermal conductivity value (WLG), except that the insulation will have a WLG of 035.
When mentioning "laid closer together," he once said that this might provide some "preparation" in case an air-to-water heat pump is retrofitted or converted later on.
Would you recommend a floor slab insulated from below? Even without aiming for KFW55 standard?
The windows have triple glazing with a Ug value of 0.7.

What does "install in layers" mean – I’m not an expert: I believe the building professional is against it because you lack long-term experience (material compression). However, depending on the house, it does account for part of the heat loss.
The statement "maybe just a 'preparation’" is nonsense... they should specify how many centimeters or what the concept looks like.
You could ask about the extra cost for a Ug value of 0.5.

So, 18 lines as a construction description is really quite short....

It won’t work with less than about 40 pages.

It probably won’t be the entire document – ours didn’t even have 40 pages either.