Don't fly to Thailand then apply for a non-O visa. Apply for the non-O visa now from the Thai embassy, or you won't be able to open a bank account in Thailand.
In order to apply to convert to non-O visa in Thailand, you must already have a Thai bank account but you cannot open a bank account as a tourist. Therefore you need to get the visa before you travel.
Once you arrive you should be able to open a bank account with the non-O you get from the embassy. Then transfer the 800,000 baht to your bank account and you can apply for the 1-year extension after the money has been in your account for 2 full months.
if you came in on marriage visa then you must extend based on marriage. The only difference is you'll get an "under consideration" stamp rather than the extension. But that stamp is considered part of your new extension and you still don't require any extra time to apply.