Now, it's very risky to work without a work permit, even at schools in the far flung places, probably still happens but not so much now. I reckon the MoE/MoL departments read them(schools/universities/colleges) the riot act around 4 years ago about 'getting their house in order'.
When I first got here there was no work permit provided for me, and many others, teaching in 2001-2003, just sent off to the border to renew the tourist visa, and that is at a well known chain of schools. Now, that same place is even getting work permits for agency staff straight away.
The days of the backpacker/aging drunk etc teacher are not over but have been curtailed to some degree.
It appears that they have made a difference on this one. In a lot of places now, Hua Hin included I'm sure, you can't even fart without a work permit and there are a lot more hoops to jump through than before.
To get a work permit for teaching you also need the teachers license now, if you are teaching students under 17-18, no exceptions. This requires all sorts of stuff, like attending a cryptic Thai culture course that few can pass unless your Thai is as good a level as Roel or Buksi.
Definitely have tightened it up from before.
Not sure about the other sections, will leave for other posters.

Edit: Typos