for them it doesn't matter how many years you had on a Visa that is now no longer valid. Getting a new Visa can restart the process, been there done that
Yep you can, you have to start it from scratch tho. Get Visa first, then maybe you need a Thai witness when you apply for next extension, expect immigration to pay you a visit home and so on
Usually you need a TM30 when you are due to a Visa extension, when you do 90day report, when you need a certificate of residence. My IO also requires it to buy a visa re-entry permit
I'm self ensured, I don't need to. In my country I get health care for free, so again I don't need you. Go try manipulating somebody else, that doesn't work with me, kid.