To backup your database see the
Database / Postgres FAQ.
You can backup your hand history files by making a copy of the 'processed' folder (see the auto import tab for where this is defined to be), or you can use Database -> Database Management -> Export to write out all your hands from your database.
I don't know when the database backup option will be added to PT3, but I hope it will be soon - I reminded the development team about this recently.