you have to have your own account. Also some offices don't allow a switch between marriage and retirement extensions. You would have to ask your local office. You may have to start the process all over anyway.
the only way for the 1st extension in Thailand, to use income is if the home countries embassy will give an income letter, the US, Canada, Australia, UK and others do not. Your only choice then is 800k for the first year AND deposit 65k per month to switch to income the 2nd year.
yes it is correct. You have to fill the previous extension requirements in order to get the new extension. Otherwise people would not keep the funds in the account as required.