He is mailing the passport to a friend. And no: I do not know the difference. What would it be? Could you enlighten us? What could you do with my passport if I mail it to you? Nothing obviously. So ... what is your point?
No idea. The point is: the guy in question has a passport full with stamps. Only the "cancel visa stamp" is missing. So, he can mail it to his friend, that is the guy who asked the question. And the author of this post can go with the passport and the agent to immigration.
No idea what you are nitpicking about. I guess passports never get stolen. A damn bag that happens to have a passport inside gets stolen.
If you are less than 180 days per year here, than you are not a tax resident. But why do you bother? I would prefer to be a tax resident in Thailand, as the taxes are jokingly low.