That's good advice but not practical for most. You only need 500K to apply for the visa and to receive an extension not as an ongoing thing or for entry or re-entry. The documents needed to apply are also generally not needed; verbal confirmation of what you do should normally suffice (it has for me).
No. On a visa exemption you have to show proof of outbound travel to the airline. They can usually see it already if you've booked an onward or round-trip ticket with their airline.
Immigration is already stopping people though. That level of entitlement won't get you across the border. Many DTV holders have been asked to step aside and provide certain documents in order to pass the borders. Some have been asked for employment contracts, details of a soft power activity, accommodation/lodging booking and/or made to sign a form.
It's becoming more difficult. It used to be possible to live in Thailand on visa exemptions, now you have to pay a visa run agency to do that, but without making pre-arrangements life is becoming more difficult for individuals who choose not to get a proper visa.