Is 3.5 final totally backwards compatible? If not is there any documentation on possible migration issues?
You cannot use solutions created in 3.5 in earlier versions of Servoy.
And as far as migration is concerned, check the release notes. Some things that are marked as [chg] might affect you, but mostly there should be no issues.
Thanks Patrick!
Make a backup (!) of your current repository and just try 3.5. There is no way back, however, because the repository will be upgraded by 3.5.