If you talk to the Thai Ministry of Labour, they did make it a lot easier for nationals from surrounding countries to get visas and work permits. They did have a clean out a couple of years ago because many workers didn't have passports. Many had to go home to their respective countries to get passports before they were permitted to return to work in Thailand. My Cambodian wife's family all work in Thailand and they don't have any problem at the border.
Cambodians can easily get a visa to live and work in Thailand, thousand's of them do, mainly in building trades, cleaning and farming. There is a Cambodian village on Koh Chang, most of them work on building as hospitality staff. There used to be a lot on Koh Samet also.
I don't know of any Asian countries where you need a license to rent a motorbike. I have even rented a car in Thailand without having my license with me.
The pollution in some of the places suggested is overwhelming. Look at the coast between Rayong and Chantaburi or even Trat. The climate and the cost of living is much more reasonable
Airlines out of Australia are asking for a onward ticket out of the country you are travelling to. It is not difficult to manufacture one using a PDF editor.
A lot cheaper in Bali. Quite a few Aussies I know get their fangs taken care of there. Comment if you want the dentists name. She is very gentle and not expensive.
Many countries now aren't using stamps. Passports are scanned and info stored on computer. The airport I leave from in Australia there are hardly any staff. It is all automated.