After having my Hubitat hub up for a few days, I started my migration tonight, doing about half my Iris stuff, with least important first. I followed the good advice of un-pairing one thing at a time via the Iris app, then letting the Hubitat hub find the new contact, keypad, switch or sensor, and naming it the same as it was in Iris. Because I knew I was dealing with Zigbee, I made a point of adopting a plug-in switch/repeater that was on a simple schedule as one of the first things. It went pretty smoothly, I did have to reset the Iris V2 keypads though, but I needed to change batteries anyway.
During the device discovery, I just decided to exit discovery after each device was found to make each discovery session a new one. I'm not sure if that was noted anywhere, but with my day job recently i had to fix a ZigBee mesh network for a large number of data loggers, and that discovery tool did better if each discovery was a new discovery session. It seemed to work fine, I got 10 devices unpaired, discovered and named in 30 minutes, and played with the local dashboard a bit to see my devices. Because I was working with least import first, I did not have pressure to meet any WAF, and I could learn as I go. I'll move my security portion of Iris last, as the Habitat forums are working through the problems we Iris orphans are having.
Habitat is different, but the forums are full of people who want to help, and there are other Iris users migrating, and finding ways to make things work. Give it a few evenings, that's my plan, otherwise, add to my Ring doorbell. Post here if you decide to get rid of that hub, you may find a buyer pretty quickly.