Additional Costs Statement - How should the list be created?

I do not know if that is even permissible. The laws clearly regulate which costs must be charged as additional costs and according to which allocation key. Regarding the heating cost allocation, I found the following: „Ansonsten gilt immer die Heizkostenverordnung. Danach muss der Vermieter mindestens 50 Prozent, aber höchstens 70 Prozent der Heizungs- und Warmwasserkosten nach Verbrauch verteilen.“

We include things like chimney sweeping, snow removal, or heating maintenance in the rent. Also the property tax or the insurance. This is then somewhat higher, but these costs simply belong to the house or the apartment. This is just fixed.

Mistake ... insurance can increase, property tax can be calculated differently. That is why they belong to the additional costs and are charged.
Everything that can be billed according to the Operating Costs Ordinance should therefore not actually be included in the actual rent price, but rather in the additional costs.

If you communicate this clearly with your tenant, it works. They also like it when, similar to an all-inclusive hotel, there are no nasty surprises at the end and the utility bill is short and simple. And understandable.

Whereas I find the last sentence unfair, the one about the 30% due to basic heating costs.

The background is that in a multi-family house the required heating load per apartment is not the same. Whoever lives at the top corner has to heat more (for the same result) than the one who lives inside downstairs. And everyone somehow heats the stairwell as well. Therefore, part of the heating costs is allocated proportionally based on living area and the other part according to individual consumption (heat meters or evaporation tubes). That’s fine as it is. I also recommend going to Haus & Grund. Otherwise: Have you never been a tenant yourself? Have you never received and checked a utility bill? That’s actually how you learn ...