What steps should I take after my 30-day visa exempt status expires while applying for a retirement visa in Thailand?

Apply for a Non O visa. Go to your local Immigration first to get their version of what you need for the application. It may well differ slightly.

You go to your immigration office and get the hand out listing the documents required to get a 90 day Non-O visa,

and

when you come back from Singapore on a fresh 30 day free entry stamp you get those documents together & go apply for the Non-O visa for 2000baht,

Then you wait the under review period (usually 2 weeks) and go back get the Non-O visa w/a new 90 day stamped inked in, AND while you're there you get the hand out listing the document requirements for the year extension 🙂

Then wait until your 800K baht is seasoned in the bank account in your name here for 2 months and you have 30 days or less left on your 90 day Non-O stamp then go to the immigration office and apply for the year extension for 1900 baht