The first thing i had to figure out was how to go about installing the whole thing.
Our envorionment is basically completely virtualized, so creating a new monitoring-VM from my favourite debian template only took a few minutes.
Luckily I figured out really soon there is such a thing as director for icinga (see https://github.com/Icinga/icingaweb2-module-director) and that
a) it seems a good idea to use it
b) it’s probably best do do everything with it, so no manual configuration at all
After looking a bit I found an install guide that explained (most importantly for me) how to clean up the default icinga2 config so you can actually start with director with a clean canvas. It’s for cent OS but that hardly matters, you only need to add the apt source (deb http://packages.icinga.com/debian icinga-stretch main) and install icinga2 and icinga2web packages. Then pick up the guide with the cleanup of the stock config and adding the director.