For the moment you won’t be able to reliably control this fan via Smarthings, unfortunately . It’s not a huge project to get this working, it’s just been delayed because it’s a relatively rare setup. I just need to make the mappings from “SetSpeed to X” -> “Increase Speed by Y” or “Decrease Speed by Z”.
Adding the “My” button: yes, that could be done. The initial device handler I created for blinds/shades had the “My” button but it was a bit buggy, so I went with the more straightforward switch to start, with the intention of returning to add the “My” button later. I’ll revisit this soon.
As for Google Home, the phrasing is
"Set <device name> to favorite position"