Are all my documents backed up in iCloud?

iCloud does not provide general backup for your Mac. Your iWork and TextEdit documents can by synced to iCloud, so they will be on the server; but other documents will not be there. If you want online backup you will have to look for a third-party solution - some options are examined here.

However iCloud will back up your iOS devices, though you can't do so or restore selectively: if you need to restore it's the entire backup.