You can get a non-O retirement visa in Thailand. You need 800k THB in a thai bank account in your name. Go to the immigration office to get a list of requirements (letter from bank, copies of passport, etc).
That's not accurate as far as I know. The validity depends on the country that issued the IDP. Mine was 3 years. Thailand says that for long-term stay, you need to change it to a Thai license. With a non-O you're certainly in that category as it is a long-stay visa. A DTV is in the category of tourist visa, not sure how this will be handled.
yes it might have some limitations. But then again if you're here 6 month at a time, do you really need a driver's license for example? Just get an international driver's permit in your home country. Bank account is probably the trickiest one, you might need an agent.
to make sure the hotel filed the tm.30. some hotels or especially Airbnb's don't, even if they are obligated to do so. If there is no valid address registration (tm.30) for you, you won't get anything done at immigration.