Whonix networking option

In the settings for any qube, you can view the template dropdown menu and the networking dropdown menu. One of the Networking drop down options was sys-whonix. I wanted to learn more about what this option does so I looked at this article: https://www.qubes-os.org/doc/networking/.
Unfortunately I could not find any explanation for sys-whonix there.
What does the sys-whonix networking option do? Does it route all traffic through tor? Could I make a new qube with my own iso and route all of the traffic through tor with sys-whonix?

Does it route all traffic through tor?

Yes

Could I make a new qube with my own iso and route all of the traffic through tor with sys-whonix?

AppVMs based on whonix-ws-15 are better for this. For example, they are configured for UTC timezone, so they don’t leak your true timezone. Also, if your custom HVM ever connected over clearnet in the past, it may have your clearnet IP stored somewhere inside.