What are the requirements for Australian retirees to obtain a retirement visa in Thailand?

Yes , you are confusing two elements you don't have to do the 65 k , if you do the 800k in the bank account , so you have that well and truly covered , easy , If you did wish to do the 65 k , then ( obviously ) no , but it's one or the other .

There is a 10 year visa available to Aussies. 5 +5

Think you need to be in Aus to get it. Sydney embassy

You are mixing up two ways you can show proof of funds (actually 3 ways).

You can bank 800K baht in a thai bank account in your name only and use that to apply for both the 90 day Non-O visa and then the year extension after that

You can transfer in to the country a minimum of 65K baht a month each month every month and use that for proof of funds

OR

you can use a combination of banked money and monthly income to meet the 800K baht total for the year

Seeing as you have several million baht in a thai bank account already you can just use the banked money method without any issues here at all

It's one OR the other, not both.