yes for an extension funds need to be in Thailand. But you can get pretty much 2 years out of a Non-OA if you border bounce just before it expires and have insurance cover for the 2nd year. To avoid bringing funds to Thailand you can then return to your home country, apply for a Non-OA visa, rinse and repeat
If you come in visa exempt you have to apply for the 90 day Non-O visa at your local immigration office and only when down to the last 30 days of that will you apply for the 12 months extension of stay. Easier to get the Non-O before you come
Depends on what you call a retirement visa. The Non-OA which you can only get from your home country allows you to keep all your funds offshore. The Non-O requires funds in Thailand unless your embassy still issues an income certificate which most don't
depends where they're running to I guess. The graphic talks about the Sa Kaeo borders. Some others are also closed but I don't know if it applies to all
visas are issued with a 90 days validity but when you stamp into Thailand within that period you get stamped in for the period of the visa. Its simple to plan