It has nothing to do with how long the DTV lets you stay. The DTV is specifically called a tourist visa in the law that created it, and the banks are not giving or keeping accounts for tourists.
IMMIGRATION will not let you pass without a TDAC. So it doesn't matter what government agency requests the information, it is REQUIRED BY IMMIGRATION to enter Thailand.
It's only Mandatory if you start filling that section out. If you start, click the "clear" button next to the air, land or sea selection and it will go back to not mandatory.
Get yourself situated. The bank will want an address and may even ask to see your lease.
That being said, you only have 30 days to get your bank account opened and get your money transferred. That's because in order to apply for the extension, your money must be in the account for 2 full months already. That means you only have 30 days to get that done or it won't be in your account long enough
Anonymous participant every embassy is different and we don't have many reports from Yangon. So these are general answers and might not be correct for Yangon.
1) either should be fine. In Laos after you go in to pay they then schedule an interview. I don't know if Yangon will be the same but part of the interview is them asking you to open your banking app to show the balance at that moment.
2) more than they ask for shouldn't be a problem
3) 6 days isn't very long. They might not even look at your application for a while after you pay but they can see when you submitted your application.