99% ? must be a special kind of people you hang around with 😉 No seriously, that number seems a bit high to me. I only know a few who are that irresponsable. I am no friend of insurances, but health should be protected.
Regarding employment, there is no difference between visa exemption and the DTV, both prohibit employment. You can indeed get into a lot of trouble when working with a Thai entity. The never cared though if you work online for foreign clients or employers.
Depends. If you dont have an extensive record of stamps from the past, especialy in Covid times, you should be fine. But there are many immigration officers in a bad mood out there. Especialy If you enter via Bangkok or Phuket airports.
My history is not clean (long overstay years ago), but I didn't have any issues with the DTV (I had many with tourist visas). I think it mostly depends on the immigration officer (mood)