Construction costs are currently skyrocketing

Does the AVBFernwärmeV also apply to district heating or is there something else?

The industrially managed potato field is simply not a valuable habitat. My garden will easily surpass it in terms of animal-friendliness.

This is mandatory for residential units. Running water is included, as well as a drain into the sewer system. Cooking facilities too. Your nice-to-haves are not. A construction project where a kitchenette must be drawn in the building application, as long as it is an apartment in the legal sense, is often financed by the bank exactly for that: an apartment in the legal sense. If you omit the kitchen, as Spartan as it may be, it is not an apartment, in this case a residential building. A kitchenette is sufficient, for example. There is no opinion on this, it must be seen objectively.

I took out 350,000, repay 3.5% at 1% interest rate... equals 1,300 EUR per month for 25.5 years.

I hope you have fixed the interest rates for more than 10 years. 1% is historically low if you look back 15 or 20 years. 2.5% is still good. ;)

Sorry, but I know at least 2 building applications in which no cooking facility is drawn in, including mine. There is exclusively the specification of where the sewage connection goes. Nothing more.