The visa is irrelevant to your question. Look in your passport, and find the date on your most recent stamp which is your permission to stay. Whatever date is on that stamp is when you must leave. You have to leave by 11:59pm that night.
Yes, I went back into Wise and saw that and deleted my post. 2 years ago they changed it to 50,000 baht, but it appears they've since increased it to 500k
Your friend is applying for the wrong visa if they are asking for proof of medical insurance. The only retirement visa that requires that is the non-OA visa, and that's not the visa that most people want. It has high requirements like mandatory medical insurance, health certificate and criminal background check.
Most people want the 90 day non-O visa, which has none of those requirements.
Not an extension, you certainly cannot. For the initial 90-day visa from a Thai embassy then yes, you can do that. Because an embassy would not expect someone to have a Thai bank account to travel to Thailand. But once you're there, it's Thai bank account or you're leaving after 90 days.
A typical tourist is whatever the immigration officer you are standing in front of says it is. I do not have the definition for each and every immigration officer, sorry.