don't try to make up situations that weren't mentioned at all by the OP. There was no mention at all that his visa was expired, and he was on his final one year entry. You made that up to fit your agenda.
not at all. He's changing to a type B extension from a type OA entry. He cancels the OA, and immediately applies for his type B. He shouldn't have to leave.
you are correct in that respect, but his isn't expiring, he is cancelling it. There is a big difference concerning the 7 days to leave stamp. If he wants seven more days just wait seven days to cancel it. He's taking a job. His current one year entry isn't expiring. There is a big difference.
it is not as difficult as these comments are leading you to believe. You do not need an agent. Immediately get a Thai bank account in your name only, and get the bt400,000 in it, and it doesn't matter where the money comes from. As soon as you have that done, with copies of your wife's ID, and your passport, bank statements showing the money is in the account, and a letter showing it is your account, and finally copies of your marriage license and amphur registration document, you can go to immigration immediately and get your type O 90 visa stamp. This gives you 90 days for the bank money to season for two months, and to get the rest of the documents together. When the money's been in your account for two months, and you have the documents from the list immigration gave you, you can apply for your one year extension. Remember to keep copies of all the documents, as in following years all you'll need is updated bank letters, and pictures. Everything else is the same, unless you move. Most of the documents you need an agent can't help you with so don't even bother with one.