If a Zigbee device is "healthy" (online) when un-paired from ST, it should reset itself and be ready to pair to a new hub. Otherwise, the process for resetting a Zigbee device yourself to do the same is usually pretty simple. Z-Wave tends to be a bit more work, as you know, but again they're usually fine if you politely exclude them first. I moved from ST to HE a couple years ago and have heard many stories from people who have done the same. There's no right, wrong, or easy way to do it. :) The only thing to keep in mind is that as you build one mesh, you're destroying the other. You may also wish to consider if/how you want to move automations: with the device (in which case you may want to move one room at a time, for example, so you can get everything set up again) or keeping the automation on ST while moving the device or vice versa (HubConnect was not available when I started but would be an option for this now).