So this would be your first year on the OA? If you leave and come back in, before the visa expires, you would be stamped in for another year without having to put any money in a Thai bank account. Although, the insurance would still be required though. Or leave and come back in to get a NON O, with no insurance required. Good luck.
He just needs to take notice of the expiry date of the tourist visa (I am assuming exemption and not visa). Then he needs to go to immigration at least 15 days before his stamp expires, use the 800k in his bank as proof for a 90 day NON O, then get a year extension of stay After that.
You mean when should you apply for a NON O. ASAP. Limit is usually 15 days minimum before your stamp expires. In some offices the 800k money needs to be seasoned. But most not.