Unless you’re an expert, this is a bad idea. Just use Whonix instead. You’re making things way harder than they need to be. The devs have already done the hard work for you and packaged it into an easy-to-use solution. Besides, your DIY version will probably be far less secure, because anonymity is a much more difficult technical problem than most people realize.
This is like trying to build your own airplane from junkyard scraps instead of simply booking a cheap ticket from a commercial carrier.
If you do want to play with Qubes networking you can still use that
article as inspiration.
When it was written, Whonix was not part of Qubes, but the fundamentals
of using different networking paths remain.
Back then, netvms were a special breed of qube. Now you can turn any
qube in to a netvm by setting provides_network True in qvm-prefs, or
“Provides Network” in the GUI qube settings.