The MFA has nothing to do with extensions. That's immigration which is a completely different government agency.
The money must be in the name of the person applying for the extension. Some immigration offices might accept a joint account but then the account needs double the money. Other immigration offices won't accept joint accounts at all. Each immigration sets their own policies. The only way to know for certain what your immigration office needs is to go there and ask them for their handout to apply for a 1-year extension based on marriage to a Thai.
This photo shows general guidelines but each office is different
it's a 90 day visa based on being over 50 (retirement). When you arrive in Thailand you open a bank account and transfer 800,000 into your Thai bank account. Then you can apply for a 1-year extension every year.
Use the message button on that page. And yes, although it seems odd, that's actually the best place to get a reply. It seems like most Thai embassies ignore e-mails and don't answer calls, but they actually pay attention to Facebook Messenger. In my case they didn't even reply when I sent a message but my visa was approved the next day.
Is there a reason you are applying for the non-OA visa? The VAST majority of people don't want the non-OA visa, they want the non-O visa that they will then extend annually in Thailand. The non-O doesn't have any of these requirements except for proof of funds. No insurance, no medical check, no criminal background check.
As far as your questions, if you want to use your own insurance then your insurance company has to fill in and sign the form. There's about a 0.
*****
% chance of that actually happening, which means you have to buy an insurance policy from the list of companies on the approved embassy list.
Normally 10-15 business days. Though they might have slowed down in anticipation of Songkran and Easter. There was also another Thai holiday at the beginning of the month.
You can always try sending them a Facebook message asking about the status. Just keep it concise, your name, passport number, application number, and just ask for a status update. But I don't think they'll be open much this week between Songkran and Easter.