I don’t have 120 devices but I have transitioned what I have to ST from Wink and then I from ST to a new ST account. First, use the information in ST to document everything that you have going on now. I used an sortable excel spreadsheet to document all my units, unit types, unit names, associated smart apps and scenes. That will make it much easier to make everything operate the same way on whatever new platform that you migrate to. I would exclude all your Z-wave and reset all your Zigbee units prior to getting started. It will make it much easier than doing them one at a time while you’re trying to set everything up. If new your controller is wired, get a very long network cable. While the Z-wave mesh works extremely well once it’s established, pairing always works better when the hub and switch are in the same room. Most of this is common sense but I figured that I’d post it anyway.
If you do it all at once, my last bit of advice is to send your family on a weekend vacation during the transition. You can also do what I did and do it bit by bit. I did all my Z-wave stuff and left all the Zigbee on the old hub for a while. I had no problem using both hubs. Everything still worked with my voice assistants which is how my wife interfaces with most of the home automation.
I was beta tester on the original Homeseer program back in the 90s. It has grown a lot since then but it’s a little pricy for me now. I’m thinking about trying Hubitat.