@dh024 Thank you for creating this excellent guide, and for sharing your automation script. 
Hope you don’t mind if I expand on one of your points:
I would add a fourth method (which I currently prefer), available for Windows users:
Install the portable Desktop app either on a USB drive or on your PC, and leave it logged in but locked (using the Master Password) when not in use; then periodically unlock and sync the portable app to get an updated copy of your encrypted vault saved in the .\bitwarden-appdata folder. If you do this on a USB drive, then the USB drive itself is your backup; if you do it on your PC, then your encrypted vault will be backed up anytime you back up your computer hard drive.
If you ever need to restore your backup, then make sure your device is off-line, plug in your USB drive (or restore your backup of the local .\bitwarden-appdata folder), and unlock the portable app. Now you can use any of the 3 export methods described in David’s guide.
I haven’t fully optimized the above technique — it is possible it can be made to work using the regular desktop client (instead of the portable one, which is only available for Windows), and it may be possible to make this work without leaving the portable vault logged in (which would provide additional security).
Would welcome any feedback on this alternative backup approach.