I reccomend using a site like https://jsonlint.com/
it will help you find the syntax issues.

Visibility has an extra , after "lan":true
Visibility is missing the , after the }

Admins has an extra , after it.

every {} indicates a group of name-value pairs. every pair should be separated with a ...

It sounds like it doesn't recognize the json file.
Its easy to break the json file, make sure your not missing a quote or comma.

when adding admins make sure its looks like this
"admins": ["name1","name2","name3"]

the file should start with a { and end with a }
The rest of the file Every line ...

it looks like the type of compressed file changed.
try sudo tar -xvf /tmp/factorio.tar.gz -C /opt
you may have to rename the file to .xz first but that may not be required.

I just verified this works and I updated the document.

I plan to split out the ubuntu setup from the factorio setup and update the document to 0.15 when it comes out.
I can make this part of the update.

would anything need to be changed to do this in Debian?
Ubuntu is based on Debian, I have not personally used Debian so I can only guess but you may need to install the software these commands use before you can use them. you may also be able to accomplish the same things with a different command ...

I created a guide on how I set up my server for Factorio.
It is a full guide from beginning to end including installing Ubuntu.

It includes the information you will need to set up multiple Factorio servers running on one Ubuntu server.
I have verified it works with 0.14.21
https://1drv.ms/w/s!Am6ec ...