So a visa exempt entry can only be extended ONE time for an additional 30 days.
Currently there are "60 day covid unable to travel extensions" that is a separate extension from whatever visa you are or where on. The only extensions that require you to use the same office twice are yearly extensions of stay, or extensions where you're given an initial "under consideration stamp" and told to return in 15 days.
Finally, No. Visa exempt entry, tourist visa, or covid extensions do NOT require health insurance or onward proof of travel to extend.
I have krungsri, it's working fine. But for future reference, I always like to keep a few thousand baht in cash on me, and a little more in my condo. You never know when stuff stuff will stop working. Even in the US, credit card systems go down occasionally due to weather.