it is immigration and it is also the departure airport that can deny you which I also said. Actually it is because of the immigration rules that the flight companies abide by those
maybe so but Thai immigration can deny you entry if you don't have a ticket out the last day you are permitted to stay and so can the departure airport
if you do it online which I have done several years there is no problem - I live with my Thai wife when I go to Thailand and always report tm30 on her behalf
there is but that apparently depends on where you are from. I am right now applying for the non o based on marriage from Denmark and there was this requirement regarding the seasoning or requirement regarding monthly income!