You do not want to show any current income. Not only would it require a work permit but it would be taxable. Online work in the US would have to be paid and taxed in the US. Do not give up your American bank account.
Two different time points. You need the 10k to apply for the 90 Day O. After you get that, you need to open an account in only your name and deposit 800k, two months before the 90 day expires so you can apply for the annual extension.
Once you have the extension, you need to transfer 65k each month for 12 months to get your second annual extension by the payment method. After the first annual extension, you can wait three months and draw your account down to 400k, after you get the extension on payments, you can draw it all out but be very careful about managing the transfers.
If you have the money, it is easier to just leave the 800k in the bank and live off the transfers. You can live comfortably for 65k, at least outside of Bangkok, Phuket and Pattaya.