If you get the 60 day visa exempt stamp and extend by a further 30 days at the Immigration office, Immigration class you as a tourist. If you then attempt to enter again on a visa exempt stamp, Immigration rightly consider that after on 90 day stay in the country that you are no longer a tourist but that you are attempting to live long term in the country. While there is no legal limit to the number of Visa exempt entries, once the Immigration officer believes that you are no longer visiting the country as a tourist he will deny you entry. If you have already stayed for 90 days on a visa exempt entry, then in future to guarantee entry into Thailand, you need to obtain a long term visa suitable to the reason for your stay. This applys regardless of if you current entry is by air or by land.
I am a 77 year old Australian living in Chiang Mai, Thailand for over ten years. I self insure for medical. I have a reserve in my bank account to cover at least one month hospital costs in a private hospital. If that proves insufficient, I would attempt tp fly back to Australia where my medical treatment would be free.
As long as the Immigration officer, after reviewing the posters stay history, accepts that she continues to be a tourist. Otherwise he will deny her entry.
If this is your third visit within a 12 month period, the Immigration officer could easily believe that you are no longer a tourist and could deny you entry unless you have a visa valid for the reason of your stay. Be warned.
1. Yes, I suggest that you apply before arrival. 2. Once you are here and have your Retirement visa, then you can go to Immgration and purchase a single or a multi re entry. 3. There is no m inimum stay requirement. 4. It is straight forward and simple to do yourself - why pay an agent extra money.