You could, and you wouldn't even need to go home. You just need to leave Thailand to apply for the DTV. But that won't keep your bank account safe. If they decide to update your KYC or you lose your ATM card, get a new phone and run into complications with the app and need to go into the bank, or any other number of things, you might lose your bank account when they check your passport.
I think it's safe to assume you are not actually eligible for the O-X visa. There's a reason no one except Australians use this visa. The consulate in Australia is the only one in the world that lets you apply with money in your home bank account. For every other Thai embassy/consulate, you must show proof of 3 million baht in a Thai bank account. Do you currently have 3 million baht in your Thai bank account? If not, you are not eligible.
Get the 90 day non-O visa like most people. That is what you can extend annually in Thailand. If you get a non-OA, the agents aren't going to want much to do with you since that one has mandatory insurance every year and you're also going to have to do a lot of paperwork in the US to apply for it.
The requirements for the non-O are trivial to obtain from the embassy, and this is the type that agents normally offer for visa/extension in Thailand.
has nothing to do with that. Residence certificate is required to get a license regardless of your visa type. And Bangkok has issued CoR for tourists for over a year now.
You write them a sponsorship letter as the primary DTV holder and state you will be responsible for their support, and you send your banking information again.
Some embassies will require an additional 500k for each dependent, while some will be fine just your 500k for yourself.