Should I apply for a Non-O retirement visa now or arrive visa exempt in Thailand?

The other option (if you don't get the 90 day Non-O in your country before you come here) IS

get a single entry tourist visa

come in get stamped in for 60 days

1 - open the bank account transfer the funds in from abroad

2 - go apply for the 90 day Non-O visa at your the immigration office in the area where you live for 2000baht

3 - wait for the under consideration period to run down (usually 14 to 20 days)

4 - go back get the Non-O visa and 90 day stamp inked in

5 - wait until your funds are seasoned the 2 months

6 - go back and apply for a year extension for 1900baht

I say get a single entry tourist visa because that gives you 60 days when you stamp in and because you need a minimum of 15 days left on your stamp to get the Non-O issued in country (Chiang Mai is 21 days)

This way you have time to your shit together, get the account open and still go apply for the Non-O

Get the 90 day Non-O visa based on retirement in your country before you come here. You can use the funds in a bank in your country. Get here, get stamped in for 90 days, open a bank account, quickly transfer in the 800K baht, wait 2 months for it to season then apply for the year extension. That's the easiest way to do it