What do I need to know about obtaining a marriage visa in Thailand after arriving on a tourist visa from Australia?

To get a 90 day Non-O marriage visa OUTSIDE of Thailand requires a person to submit a collection of documents to the local Thai consulate (the documents vary depending on the consulate used), and the visa WILL BE granted; may take up to 5 days.

To get a 90 day Non-O marriage visa INSIDE of Thailand requires a person submitting a collection of documents to the local immigration office (assuming the immigration office sells the Non-O visa). The visa WILLBE granted the same day.

To get a one year extension of stay requires a person submitting a collection of documents to the local immigration office. The immigration office will review the documents, they will review the documents, and grant the applicant an "under consideration" stamp which is valid between 14 days to a month (generally, depending on the immigration office). IF the extension of stay is approved, they will be granted the remaining validity of the time. If it is not approved, they will have 7 days to leave the country.

Can you return to Thailand before your OA expires? If so with 1 year insurance, you get stamped in for another year. That's what I'm doing

You can’t extend your OA visa outside Thailand but you could apply for a new OA visa.

you can buy a tourist visa from the thai consulate get here, get stamped in for 60 days, get your shit together, open a bank account transfer in the funds, get your documents sorted to get a marriage to a thai national registered at the Amphur then apply for a 90 day non-O visa based on marriage.

There is no seasoning of the 400K baht when you first apply for the 90 day non-O visa based on marriage. You just show it in your account on the day you apply for the visa.

The key to the whole scenario is how fast can you get your shit together, get the account opened, get the documents to get married, GET married, and still have at least 15 days left on your current stamp so you have time to apply for the 90 day Non-O visa at the immigration office.

The 2 month seasoning only comes into play when you apply for the year extension AFTER you got the 90 day Non-O visa issued.