And do the 14k for the connections (presumably on your property) also include the costs for the installation of the transfer storage tank? This usually remains the property of the district heating operator. But of course, you are allowed to pay for the installation.
The supply and service boundary for district heating is specified by each provider in the general technical terms and conditions (TAB) or at the latest in the heat supply contract. Sometimes this is the main shut-off valve on the building side, in which case the customer is responsible for the entire system technology including installation inside the building, and the TAB specify the return temperatures to be maintained (and accordingly the dimensioning of the transfer station). Sometimes there are concrete specifications for the station (type, capacity, manufacturer) and sometimes the provider also takes over installation and operation. The latter is especially the case for direct networks where there is no separation between network water and heating water inside the building (rare in new buildings). For cost calculation, the original poster should inquire with the provider, as the transfer station including installation costs around 5-6k euros.
KfW40+ and district heating are not contradictory, by the way. The decisive factor in heat delivery is the primary energy factor fP of the heat. This can also be 0.0 (no typo) for purely natural gas-fired combined heat and power plants (CHP), and is often between 0.0 and 0.4 for larger plants. Whether that makes sense is another matter, but that is how it is. The price escalation clause is fixed, but the gas exchange price stored there can rise – and the 2022 price is based on the exchange indices from 2021, so be prepared for significant increases in 2023 and 2024. However, with KfW40+, this is not so serious since the heat demand itself is very low.