actually, and you should know this already, it's called a type O extension based on Thai wife. Not using the correct terminology confuses people. The same with Visiting Thai family. That's what it is called. To use anything else confuses people.
he's on a single entry he received without having bt400,000 in the bank, and from the sound of it he still doesn't have the bt400,000 now required to get another type O 90 day visa from outside of Thailand, and thus doesn't have the bt400,000 to get the one year extension.
if your letter does not state that you can work remotely you'll be asked again to provide that document. The embassy doesn't assume anything. They want it in writing.
don't make it complicated. Write a letter on your company letterhead stating that you are contracted to work remotely, and sign it as the owner. It is that simple, as the only legal entity it goes to is the Thai embassy.
being that you can only get the OA in your home country,when it expires you can apply for a new OA inside your home country again. There is no limit on how many times you can do this, as long as you maintain your insurance.
no, the OA can be extended inside Thailand for another year exactly like Graham explained, and it is the same method as a type O extension, with the insurance requirement added. To switch to a type O you must exit the country when the OA expires, and start all over getting the type O 90 day entry stamp first then the one year extension. You can extend the OA inside Thailand, but it is no longer multi-entry unless you also buy the multi-entry re-entry permit, and it is only valid for the one year extension. You can not leave before it expires and return getting another one year stamp. It no longer works that way when extended inside Thailand
you can extend, but to do it you need to present all the documents you used to get the DTV, and they must be updated. You don't need any documents when you exit Thailand and return, just your DTV pdf printed.
Umm, unless something has changed with the Bangkok Bank app you can only get the last three months of statements, not 12 months. If you could get 12 months from the app immigration doesn't accept them. You also need the letter from the bank stating the account is yours.