As a first step, I had installed remote controlled (Z-Wave) thermostats for my radiators. In addition, I installed Devolo’s Control Center and registered on its website for access to the control center. I had thought, from a prior email exchange with Devolo’s support, that it would not be necessary to use their web service. However, I was not able to identify (or find documentation) about a web server or some other management UI on the control center, so I decided to go through their website. I resent this, as I didn’t necessarily want them to have data on my home configuration, but it was the fastest way to a working set-up.
The first step was still a hardware installation step. I needed to plug-in the control center box and connect it to the Internet. My current solution below utilizes a Fritz! product, Ethernet over power-line. The Devolo Control Center comes with its own built-in Ethernet over power-line support and is supposed to be plug compatible with the Fritz solution, alas, this did not work out of the box. It is the one remaining problem to solve for me, later.