What are the steps and requirements for converting a Non-OA visa to a Non-O visa for expats in Thailand over 50?

For a Non-OA to Non-O, based on over 50 years old, conversion. I have reviewed prior posts, including the excellent guidelines, but would appreciate some guidance on the following.

Currently on an extension based on my 2018 Non-OA visa, USA passport, extension valid until October 27, live in Chiang Mai.

The timing is very important to me since I want to have my annual extension renewals due about mid-February of each year, for which I can apply up to 30 days in advance in Chiang Mai. I leave CM each year for 2-3 months, usually in mid to late February. Once I am clear on the items below, I can calendar it out to figure out the best time to leave the country without a reentry permit and return 1 to 2 weeks later on a visa exempt entry - which likely will be 45 days if I return in October

1. After returning, I get 30 or 45 days and will soon apply for an in-country Non-O based on 50+ years old, at least 21 days before my permission to stay expires. Question: will that 90 day Non-O begin on the date of application or approval, or will it start at the end of my visa exempt expiration date?

2. When I apply for a 1 year extension of stay, based on that 90 day Non-O, will the extension begin on the date of application or approval, or will it start at the end of the 90 day Non-O expiration date?

3. Re: requirement of proving origin from funds out of the country. I did this 2 years when I got my first OA extension 2 years ago. The deposit has remained in my Bangkok bank account. Do I need to prove the origin again? Can the bank provide me a letter recertifying the origin from a deposit made 2 years ago?

4. Am I correct that no health insurance at all is required?

I am aware of the other documents and requirements for applying. Thanks for your advice.