If you already have the 90 day non-O visa then you don't have to worry about source of funds. But you are not getting any 1-year visa. You will be getting a 1-year extension. There is a huge difference, and you need to use the correct terminology.
That depends on if you are actually asking about a non-O VISA, or are you actually asking about the 1-year extension based on retirement?
If you are talking about applying to convert from tourist to a 90-day non-O visa inside of Thailand at an immigration office, then the 800,000 must show as an international transfer.
If you are actually asking about the 1-year extension, then there is no requirement for the money to show as an international transfer.
I know. And those people can request to have their limit increased. But this person opens a new account and then immediately requests a limit in crease. That's suspicious.
The "limit" which isn't actually a limit is mostly a warning to people abusing visa exempt. If they enter and stay 60, or 60+30, and then leave and return and stay 60 or 60+30 again, they're not likely to get an other visa exempt. But if they are coming for a week or two and then leaving, coming for a week or two and then leaving, no problems. There are people who work in the region that have 1-2 weeks off every month and have no problem entering Thailand 6-10 times per year.
You don't think it's a little suspicious if someone opens a new account then immediately requests a higher transfer limit? Use the account for a while and show that you need more than 50k per day. That would involve hitting the maximum multiple times per month and nothing wrong happening with your account.