How to start a mixer node?
Well, you have to write a piece of software that complies with the spec.
Unfortunately, I don't have access to either the specification or the reference implementation.
I will try to reverse engineer it soon.
If someone came up with a secure simple way to let people run mixer nodes for free a lot of people would voluntarily do that. It would certainly get good coverage in the alternative media of countries whose politicians are obsessed with control.
A lot of citizens in countries like Iran and North Korea and Saudi Arabia and the United States are concerned their governments might snatch their coins or play other anal control games with altcoins.