But as

@Brandon ***********

says, it is hard to stay long term in Thailand. But you could do it for maybe a year on tourist visas/exemptions before having to start thinking about longer term visas options.

Thailand and Vietnam are the only countries you mentioned that are actually in SE Asia.

And out of what you listed, Vietnam would be the least expensive by far. But Thailand has the better infrastructure.

Oooh, this reeks of a denied entry at some point. As others have said, try for the multi entry visa instead of all the extensions But you DO have to leave the country before 90 days is up each time you enter during the visa period.

It is the education visa that raises red flags for Immigration. Do you actually intend on attending all the classes? If it is your future plans to reside permenantly in Thailand, I might think twice about the ED visa.

If you have the funds, Elite Visa is probably the least hassle long term, as it is basically a high end 5 to 20 year tourist visa. You don't have to worry about check ins, as I believe any that are needed (might be a yearly one) are arranged for you, and they give you some privileges at various levels. It is especially good if you travel out of the country often.

Kuala Lumpur and Singapore are the easiest. Why not spend 2 nights. Both are nice cities. Cambodia, Laos, (For Americans, Vietnam), Indonesia, all need visas.

Yes! The 2 easiest and shortest, with no need for visa for many travellers.

Getting harder these days. Your chances increase if you actually have a bill that you pay monthly (like cell phone, etc), or if you are renting a condo for a few months.

Some visas require it, but normal tourists do not. However, unless you have plenty of cash to cover expensive medical complications, and someone you trust to handle the costs/payments if you are incapacitated, then insurance is a no brainier period.

Other than actually doing it over and over... Research stuff, join groups like this, read the posts and comments, and re-research every 6 months or so, as things can change.

If you are renting a condo longer term, it seems to be easier, as there is some sort of lease or agreement.