Hey
I just got the U400, U100 and M200 hub and looking for recommendations on sequence to install so that I can get them all running in Home assistant as well as apple HK. I know you don’t need the hub for the U400 but I already had it and I think you need it for then u100.
I have a single U400, multiple U100s, Hub M3, and Hub M2, all exposed to HA via Matter integration. Add the hub to HA first and then any devices you connect to the hub will come in automatically. I can’t speak intelligently on the Apple HK as I am only using it for the FP2 presence sensors and g410 doorbell camera. You will need to install the “Matter Server” add-on in HA before adding the hub.
Installation order shouldn’t impact anything. But you can use Matter multi-admin to pair to both U400 and M200 (w/ U100 bridged) to Home Assistant and HomeKit independently.