What are the advantages and disadvantages of obtaining a three-month Non-O visa abroad before applying for a 12-month retirement visa in Thailand?

Advantage is that you get 90 days on entry, which gives you 30 days to open a bank account and deposit the money to apply for the 1 year Extension of Stay.

Disadvantage is that IF you apply in South East Asia you are depending on the requirements set by the Thai Consulate in that country.

As a rule there is no insurance requirement to get a non-O visa issued at a thai consulate (especially NONE in S/E Asia)

You see it being asked on the eVisa website when you apply but you just write N/A on a piece of paper and upload it. It is NOT a requirement to have insurance for an O visa

The upside is you ENTER the country on a non-O visa and get stamped in for 90 days so you can apply for a year extension when you are down to 30 days or less left on that stamp rather than having to apply for the Non-O visa, wait for the review period, go back and get it inked in