I run HA on Proxmox and have the old Skyconnect for Zigbee which I use via ZHA. All in basement with the Skyconnect on a long USB2 cable to keep it away from any computer interference.
I recently purchased four of the Sonoff Hydro One (SWV-ZFU) sprinkler controllers to replace gen 1 Orbit bHyves and am trying to figure out the best road forward on a second dongle to play with Z2M which seems to open up more info from the Sonoffs. Also, if it matters, I have Apple TV via Home as a Matter/Thread hub as well. Also, I'm using an older ZST10 for zWave if there are options for a multi-protocol device.
From everything I have read, my choices seem to come down to:
ZBT-2 - HA made so can support them. Newer chipset. But issues with running Zigbee and Thread simultaneously. Also still annoyed that Skyconnect didn't keep all of its promises.
Sonoff Zigbee 3.0 (E or P??) - going with Sonoff might allow me to use eWeLink but not sure if that offers much benefit. I connected to each of the Hydro Ones via BLE initially to do firmware updates and all are accessible so can do so again in the future. The eWeLink's irrigation doesn't appear to offer much over my HA automations either.
SMlight:
SLZB-07 - newest chipset. Seems to allow concurrent Zigbee and Thread but not sure if that matters with Apple Home via AppleTV as thread hub/router
SLZB-MR1U or MR3U each $100 and no clue what benefit they have over anything else
I read somewhere about a combination Zigbee/Thread/Zwave device from them but not sure if that ever made it out of early betas. My zWave stick is an old ZST10 so could use an update.
I have an old rPi running docker so I think any of these will end up plugged in there and will run Z2M in a docker container.
Some advice from someone who's been "slowly" migrating from ZHA to Z2M for the past 4 years (& still running both in the meantime)
Get a coordinator with Ethernet. Doesn't necessarily have to be PoE, but it's got a few advantages over USB. You don't have to deal with device paths, USB interference or placement restrictions. Simply stick it anywhere with an ethernet port & point the Z2M config to its IP.
Don't attempt to run Zigbee & Thread on a device with a single radio. If that's your gripe with Skyconnect & ZBT-2, the devs removed the MultiPAN option because it was highly unstable & caused more issues than it fixed. Either get 2 separate coordinators for Zigbee & Thread, or else get one of the the SMLight MR range, which has 2 separate radios in a single device. (PS: $100 is a ripoff - you can get them for around half the price on their Aliexpress shop)
That combination Zigbee/Thread/Zwave device you mentioned is this beast. Seems to be available to buy from their Ailexpress shop if you follow the link at the bottom of the page.
You don't need to run Z2M on the old Pi with docker. Z2M will happily run alongside ZHA as an HAOS app as long as you don't try to use the same coordinator for both integrations. Alternatively, since you're running Proxmox, you can fire up a standalone instance of Z2M with a single command from Proxmox VE Scripts.
Remember Zigbee is a mesh network. If you're spinning up Z2M & only intend to use it to connect to the Hydro Ones for now, you're going to run into disconnection issues unless you place the coordinator somewhere extremely close to them. Alternatively, either buy a few more zigbee routing devices for Z2M or plan to migrate a few of your existing devices from ZHA to Z2M to build up the mesh.