Is estimating KFW55 useful, or is the Energy Saving Ordinance preferable?

Good day,
we are planning a single-family house in southern Germany (Stuttgart catchment area).
It should have approximately 155m2 of living space and additionally be fully basemented, whereby it should be noted that a cellar room of about 50m2 is to be heated.
Our question now is whether it is worth going through the bureaucratic and financial effort to achieve a KFW55 subsidy.
Regarding the rough equipment of the house according to the building description:

2 full floors with hipped roof
Gas heating with solar thermal for domestic hot water heating (unfortunately, I have no data regarding the area and performance of the collectors)
Wall structure on the ground floor and upper floor made of insulated bricks (U=0.17<0.2 W/(m^2 K))
Insulation in the basement: 8cm Styrodur
Central ventilation system with 95% heat recovery
Windows currently Uw=0.95 (>0.9 W/(m^2 K)), total window area approx. 57m2, total 19 windows (excluding basement windows and the one roof window).
Roof window (only an exit hatch to get onto the roof) currently Uw = 1.2 (>1.0 W/(m^2 K))
Underfloor heating everywhere (except in the heated basement room, where there are two radiators)

What I see critically is that the general contractor is rather reluctant to build according to KFW55 because, according to him, everything drags on, there is bureaucratic effort, and he is also externally controlled.
We have to take care of an energy consultant ourselves. Unfortunately, those requested are only available from mid-January. Our offer from the general contractor is valid until mid-December.
The elements to be improved according to the comparison are: windows and roof windows.
Probably the basement insulation and possibly also the ceiling insulation to the attic (I cannot find any information about this in the building description) still need to be improved.
According to the statements of other builders, the heated basement is also problematic - would it be possible here, in order to achieve KFW funding, to only have the heating pipes installed in the floor to keep the option open later to add radiators?

Now the question:
What would you do? Try to achieve KFW55 to get the 18,000€ subsidy or just build the house as it is?
Many thanks in advance for reading and your opinion!

The consumer advice center has a really good telephone information service on the topic of energy consulting. I initially had contact and it was really very helpful. They might be able to help you quite well. In principle, it should definitely be feasible with Kfw55.

We are building a single-family house with a basement and 2 full floors with KFW 55. The surcharge for "Maßnahmen" to achieve KfW 55 is 8,000€ for us. We had offers between 7,000€ - 9,500€ from various GUs.

So effectively, about 10,000€ remain for you. If you offset that against the interest for the KFW loan (0.95%) and the interest you would get from a bank without KfW 55 (about 0.80% maybe?), you would still have more than enough left – it certainly doesn’t make much difference...

Besides, you have a better insulated house and potentially save on heating costs. For me, building without KfW 55 would not be a consideration at all.

I would also choose KfW, provided that the shorter KfW term in the financing does not cause problems with regard to the monthly burden and the other loan conditions are not significantly better without KfW. The additional expenses for KfW55 are certainly manageable, especially since a condensing boiler + solar thermal system and ventilation system are already planned anyway.

And even without KfW: a little control regarding avoidable thermal bridges / energetic weaknesses during construction is, in my experience, well-invested time for a later worry-free time in the house. In these areas, the executing trade often prefers the easier way with occasionally not optimal energetic execution without detailed advance planning – after all, everything later disappears under the nice wall paint.

If underfloor heating is planned throughout the entire house, then I would, if possible, not install a radiator in the basement (this can lead to a mixer for two temperature levels – a more complex overall system).

Currently, kfw55 is the sweet spot

Doesn’t KfW require at least 3% repayment? Could also be a criterion if the amount of the monthly installment is very important...