@koenkk I have been following this thread and project since you started, but I only just managed to get around to setting it up.
First battle was finding the cc devices in my study, they had hidden themselves quite well.
Then it was simple, all went according to the instructions, and apart from glitches due to my own hurried (mis)reading, it has all gone smoothly. I have three devices connected, all Xiaomi. A presence detector was the first one, all sweet.
Then my cube, which was a pain to get connected. I was disappointed that once connected it didn’t work in my kitchen, but my third device was a power plug, which once paired I plugged in half way between the server and the kitchen, the cube now works in the kitchen and a network map confirms that the cube is routed through the power plug.
Couldn’t be happier, and I still have three weeks summer holiday left!
Congrats on an excellent project.
PS. One small suggestion, on the setup page https://koenkk.github.io/zigbee2mqtt/getting_started/running_zigbee2mqtt.html it might pay to mention that the user running zigbee2mqtt needs to be in the dialout group. That may be so by default on raspberry pi, but it isn’t on ubuntu 
PPS, this network map custom component was also extremely easy to get going Zigbee2mqtt: show the networkmap in home assistant