Incorrect. A return ticket is only required if you don't have a visa (visa exempt entry). If you have a any type of visa then you don't need a return flight.
The Privilege (Elite) visa is also in the same category of special tourist visa as the DTV but there is no problem opening or maintaining bank accounts with that visa.
They added the new visa types in the Royal Gazette but the underlying law governing work authorization was not changed. The relevant law is the Alien Working Act, B.E. 2551 (2008).
Sticking to the letter of the law it's not legal to work remotely with a DTV either. The Ministry of Foreign Affairs introduced this visa and said people could do remote work but the no laws were actually changed to allow this.
Buying is no problem. Renting it out is technically illegal if you are managing the rental yourself because that is considered 'working'. But you are very unlikely to have problems, especially with only 1 property. If you wanted to be 100% legal you would have to use a property manager or a Thai person to manage it for you. You also need to file a tax return for your rental income, even if you stay in Thailand less than 180 days in the tax year.