Consider splitting "Backup/Restore" into a standalone dialog (vs Preferences)
One thing that confused me when I initially started exploring this app is that there was no mention of importing/exporting/backuping in the main menus, whether in the properties of an account or in the main UI.
Eventually I discovered (by random luck) that there are such features, but in the "Preferences" dialog.
This does not make complete sense to me: all the things I can see in that tab are actions, not preferences.
Wouldn't it make more sense (and make it more discoverable) to split this to its own dialog, to be accessed by an "Import / Export…" main menu entry?