What are the requirements for a Non-O visa extension based on marriage to a Thai wife in Nonthaburi?

You need to go to the Nonthaburi immigration office (with your thai wife in tow) and get the hand out listing the documentation you need to apply for a year extension based on marriage to thai.

The 400K baht need to be seasoned in a thai bank account in your name only for 2 months before you APPLY for the year extension.

You will need to get the standard bank letter, (the one that states on this date you had a balance of this much). MOST offices allow that letter to be up to 7 days old BUT some offices want it issued on the date you apply for your extension which is why I said GO to the immigration office before hand and find out how they do it there

Also you will need to update your bank book on the date you apply for the extension so it shows the 400K baht is still in the account on the date you apply

I have no idea what you're talking about as far as the affidavit :/ Sorry, tell me what you think that is