Since I was disappointed by the information I could get on the world scenery 2.0 build, espectailly on the machine it run on, I've decided to give some insight, on what is needed to run an osm2city worldbuild.
As of January 2020 the build is run on a server with two 8-core/16-thread CPUs and 96GB RAM. While at first the CPU seems to be the bottleneck, once you get into densly packed areas the RAM becomes the limiting factor. I've seen a single thread taking up more than
60GB of RAM so make sure, you've got enough. For larger systems I'd recommend to go with running one thread per 4GB RAM as many threads don't even need 1GB which gives room for some threads to grow beyond that. On smaller systems be sure to monitor the RAM usage and reduce thread count if neccesary.
For storage there are five 4TB HDDs configured in a RAIDZ2 with an effective capacity of just below 12TB. Currently this is more than is needed.
As of writing the global osm data in the database has a size of 2.3TB but this requirement can be lowered (with a penalty in runtime) by only importing the required area from the highly compressed .osm.pbf file. With this approach, the initial try worked relativly well on a 1TB HDD with enough headroom.