Build a multi-family house according to the Energy Saving Ordinance or KFW55?

How do you mean by "adjusting calculations"?

I mean that KFW is only a guideline that calculates and then evaluates a quantity of many things in total. Due to the factors "quantity" and "many things," a house that originally follows Energy Saving Ordinance 70 as a model can become a 55 if the components fit, and vice versa if the components do not fit. It is just a calculation for a funding standard. Whether it is economical, energetic, or whatever, it does not say that at first.

Sorry that is simply not possible to say in general. Maybe the insulation is already sufficient, maybe not. Maybe only for the two units on the upper floor. A heat pump can be cheaper than gas with ST. So either leave it as is or plan and calculate.

We will definitely calculate that and see what the bottom line is.

Above all, consider yourself how you want to design the technology.. central heating, floor heating. Is a heat pump an option or not, ventilation system or not. Photovoltaics or solar thermal or neither.

The subsidy is one-time, the technology remains.

Ongoing costs or savings are primarily determined by the technology, less by minor changes in insulation or meticulous calculations. In the case of rental, it should be robust and the ongoing costs may (partly) be irrelevant to you.

The funding is one-time, the technology remains.

A nice saying for the night, I'll frame it.

With our house, the construction of which we will finally begin soon, the main focus has always been to find the best possible balance between the factors budget, economic efficiency, utility, and desire to own. The goal was to build a reasonable new building, which, in my opinion, is already achieved with the Energy Saving Ordinance. KFW was never a factor for us, as we want to avoid any financing if possible.
So we looked at what we can have and want:
standard shell, controlled residential ventilation, brine heat pump, underfloor heating, photovoltaics, solid windows, insulation on the floor slab and in the roof with on- and between-rafter insulation.
And tada: our energy consultant calculates KFW 55.
The thing is, most of this I would never build into a multi-family house. We currently have a really quite exclusive [EW], which we will now sell.
I am sure the apartment will not sell because of the energy certificate, but because of the location and demand.
Sure, there may be someone interested in whether it is a heat pump, gas, or whatever.
As a rule, however, people will look at what additional costs they have and whether they like the place.
But I might be wrong. We will see.