What are the requirements and procedures for obtaining an O-A retirement visa in Thailand, specifically regarding the 90-day reporting and medical insurance?

If you have an O-A visa you'll be stamped in for however long you're insured for so if you just want 9 months just buy 9 months insurance (you'll probably have to use Tune as I think most of the other providers only do 1 year policies but I may be wrong). The insurance for your whole stay must be purchased up front

If you plan to enter and simply leave after nine months there's no point in doing the 90 day report as you'll never have any reason to visit immigration and the officers at the airport don't give a stuff about 90-day reports

They are so many Facebook groups about renting condos here. Where are you gonna stay?

It is a 90 day report you will need to do, not a renewal, no fee. The first report must be done at an Immigration Office, the following reports can be done on line. As far as insurance goes, I'm not sure about short period policies, but why not pick a policy and select monthly payments and then just stop paying when you don't need it.

No you cannot do 90 days at a time. When you submit your application to the embassy, they will require 1 year of insurance, because you are applying for 1 year visa.

Your insurance will also be checked when you enter Thailand, and if you do not have 1 year of insurance, you will only be stamped in for as long as your policy lasts. So if you had a 90 day policy, you would only be given 90 days inside Thailand.

You can look for a serviced apartment. But for the most part leases in Thailand are for 12 months and landlords don't want to deal with shorter leases, especially now that the country has opened back up.

It's difficult to search for places to stay as there is no centralized listing place, each agency has their own units and no access to what other agents have, so you would have to reach out to multiple agents.

The only fee is for when you first get your visa. There is no charge for the 90 day report. Health insurance has to be valid for the number of days your visa is valid. If you only purchase for 90 days then immigration will only stamp you in for 90 days even though you have a one year visa.

Normally they require insurance for the period of the visa. But its been known they only stamp you in for the period of insurance. So if only 3 months they may only stamp you in for 3 months. Others may help, this is just what I have read in the past not from personal experience