Took me about an hour for the whole process, but everything went all right.
Started with 1.8 and already had a unified storage. Pre-update, update, gapps install… restarted the phone 3 times in total. Had to do the home screen and widgets again, but I knew that was coming because of the old launcher coming back. Not too happy about that, but okay. (See here: Getting the 1.8 Launcher back - (originally: What's wrong with consistency?)) Had to log in with Google again, but after that all the apps were good. Automatic log ins, tabs still open in chrome… good stuff.
I do hope this software version is more stable. I complained about some bugs in 1.8 earlier (See this page: Bugs in software version 1.8), and they don’t seem to be adressed according to the change log, but I hope it will do.
Good luck to all other Fairphone owners.