Decision KfW55 vs. KfW40 plus

[*]Ask the GÜ for data on photovoltaics + storage [*]Have the additional costs for KfW40 plus itemized according to: additional insulation, photovoltaic system, storage, central ventilation system, other (in case there are any additional items here) [*]Have the maximum possible photovoltaic system calculated + have an offer made [*]Have an offer made for the preparation of a photovoltaic system (e.g. cable duct) in order to be able to outsource the photovoltaic system as a trade if necessary. It should not cost much but maybe the question will cause the GÜ to make a more attractive offer themselves

By the way, you can roughly estimate the savings if you compare 55% to 40%.
With one hundred euros heating costs in a kfw100 house, you save 15€ monthly going from 55 to 40.

Hello everyone,
we are currently planning our house and considering whether the additional cost from KfW55 to KfW40 plus "is worth it." By worth it, I mean on the one hand the amortization period but of course also other advantages and disadvantages, such as a central ventilation system compared to a decentralized ventilation system.
Our general contractor standardly offers the following options (alternatives are possible by agreement):

[*]KfW 55 (no additional cost): aerated concrete plan stone 36.5 cm, air-water heat pump, underfloor heating, decentralized ventilation system
[*]KfW 40 plus (€25,000 additional cost): aerated concrete plan stone 42.5 cm, air-water heat pump, underfloor heating, central ventilation system, photovoltaic + energy storage

My specific questions are:
1) What savings potentials arise due to lower heating costs, electricity costs, and feed-in tariff, if energy price increases, maintenance, and repairs / total loss of components are disregarded? I understand that many factors play a role here and this can hardly be calculated, but maybe based on comparison values and taking into account the following information, at least a rough range can be given:

[*]The house is located in NRW (mild climate)
[*]Roof orientation / pitch is almost ideal for photovoltaics
[*]The house has no basement and with the 42.5 cm stones a living area of 190 m²
[*]2 adults and 2 small children
[*]3 kWp photovoltaic, 6.5 kWh battery (assumption)
[*]Temperature in living areas approx. 23°, bedrooms approx. 21°
[*]The additional KfW funding options are, of course, known to me, but the KfW loan interest rate is less favorable than the interest rate of our bank, so the advantage would be reduced to €8,150.

2) What other advantages and disadvantages arise between KfW40 plus and KfW55?
3) Further tips for ways to arrive at a good decision?
Many thanks in advance for your assessment!
J.

Thank you very much for the many helpful answers.
Photovoltaics + storage are NOT part of the offer from the general contractor, but estimated information from me – sorry for the confusion.
I will now do the following:

[*]Ask the general contractor for details about photovoltaics + storage
[*]Have the additional costs for KfW40 plus broken down into: additional insulation, photovoltaic system, storage, central ventilation system, other (if there should be any additional items here)
[*]Have the maximum possible photovoltaic system calculated + have an offer made
[*]Have an offer made for the preparation of a photovoltaic system (e.g. cable duct) in order to potentially outsource the photovoltaic system as a separate trade. It shouldn't cost much, but perhaps the question will motivate the general contractor to make a more attractive offer themselves

Then we will see further …

[*
Photovoltaics + storage: Minimum according to KfW requirements, i.e. approx. 2.7 kWp for us
[*]Additional costs broken down (net):
[LIST]
[*]Photovoltaics + storage: €13k
[*]Planstein 42.5 cm + additional insulation: €8k
[*]The central ventilation system was already included in the price and is therefore not part of the surcharge for KfW 40 plus! Omitting it would of course be possible and would save €4k.

Thank you very much for the many helpful answers.
Photovoltaics + storage are NOT from the general contractor's offer, but estimated figures from me – sorry for the confusion.
I will now do the following:

[*]Ask the general contractor for details on photovoltaics + storage
[*]Have the additional costs for KfW40 plus broken down by: additional insulation, photovoltaic system, storage, central ventilation system, other (if there should be any additional items here)
[*]Have the maximally possible photovoltaic system calculated + have an offer made
[*]Have an offer made for the preparation of a photovoltaic system (e.g. cable duct) in order to possibly be able to award the photovoltaic system as a separate trade externally. This should not cost much but perhaps the question causes the general contractor to make a more attractive offer themselves

Then we will see further...