Of course they dont but they do know when you checked in and checked out of your previously filed TM30, which means they might want to know where you were if there's a discrepancy in the date the next TM30 is filed
The OA doesnt require funds in a Thai bank and you can get 2 years from the visa. Yes does it does require health insurance but most people have that anyway.
Yes, or get the Non Imm O in Australia, arrive in Thailand and bank the 800k in a Thai bank and then just apply for the 1 year extention of stay. Job done.