No really sure what you’re asking. Revolut (as in a physical or ecard) will work with places that accept card payments (high end restaurants and hotels and the like) but won’t work with cheaper places or street food type places.
You can use your card to get cash at an ATM but you’ll be charged 250 baht for the transaction regardless of the amount you withdraw.
Yes you can. You could have over 10m in the account and spend at will. Immigration only want to see that you have at least 800k at the time of application.
You are referring to a special visa waiver scheme that a few countries have with Thailand. That’s not a tourist visa. It’s a visa waiver. As a Korean if you bought a tourist visa prior to arrival you would get 60 days. Not that anyone would want to waste their money doing so.
Had a person today at immigration with a 20+ day overstay because they bought a “90 day tourist visa” prior to coming and wanted an extension. They hadn’t realised that a tourist visa is valid for 90 days from issue but gives you 60 days on entry.