Is an Australian marriage certificate and bank statement valid for visa purposes in Thailand?

Sadly "quick questions" don't always equate to quick/short answers🙁

if you're asking can you use an Australian marriage certificate in country so you can get either a 90 day Non-O or a year extension based on marriage to a thai national that answer is no, just that auzzie marriage certificate isn't going to cut any ice 😮 It is a multi-step process you need to go thru to register the marriage of a thai overseas.

You have to first get the marriage certificate certified at your embassy (and if your embassy here no longer does certification of marriage certificates like the US and UK stopped doing) you have to send it back to Oz to get it certified by your 'state' and after that stamped by the Thai Embassy that controls your state (either Canberra or Sydney)

THEN

You have to get that certified marriage certificate translated into thai,

THEN

you have to get that translation certified by the Ministry of Foreign Affairs

AND then finally

you and your thai bride go to a local Amphur (city hall) and register the marriage of a thai who got married abroad there. They will give you the Kor Ror 22 <- registration of thai married abroad document, and THAT'S what you need to apply for either an in country Non-O visa or a year extension from a 90 day Non-O visa based on marriage to a thai national at an immigration office inside the country

Now as far as proof of funds, seeing as you come from a country whose embassy here no longer issues 'affidavits of income from abroad' notary documents (stat decs), they stopped them at the end of 2018. Your only option for the initial 90 day Non-O visa or the first year extension based on marriage to a thai is via the banked money method and that requires you to have 400K baht in a thai bank account in your name only. To get the initial 90 day Non-O the funds do not have to be "seasoned" <- meaning they can just be in the account on the day you apply for the 90 day Non-O visa,

BUT

To get the year extension from that Non-O visa once it runs down you need to have the 400K baht in a thai bank account in your name only for 2 months before you apply for the year. You need a detail transaction report from the bank covering at least 2 months, you need the 'standard bank letter' from the bank (stating your name, balance, account number and date, AND you need to update your bank book the date you apply for the visa/extension