Also not known. Certainly need to be proved at the time of applying for the visa. I would assume that immigtation in Thailand would also be within their rights to ask for proof again on extension, if they are in doubt. And even at the airport or land borders, immigraiton officers are at liberty to ensure you have sufficient funds to support yourself during your stay in Thailand. Theory aside - I would expect that you won't have to prove anything in most cases once you hold that visa in your hands.
Not permanent residency, no (that is a different beast). But the LTR with the ability to stay up to 10 years without leaving is definitely meant for temporary residency. Isn't really of much practical consequence at this point, though.
Not regulated in the published law. Will likely depend on the consulate which you are apply at. I would assume that it needs to be in a savings account in most cases - that was the case with requirements for other visa.
The official law is published. It states exactly what I claimed and illustrates that the DTV works exactly like the METV - just with a longer validity and longer stamped in stays. So no need to debate this.
As for your other point ... well, that is dependend on how you define residency. But you are right, if opening bank accounts, getting 5 year driving licences, and getting a tax ID etc is feasable with the DTV ... then it can be seen as some sort of unofficial residency visa, yes. Strictly speaking a visa geared towards residency would allow you to stay in country beyond the threshhold of becoming a (tax) resident.
That is what they mentioned initially. There is no "price" mentioned in the published law in the royal gazette. So, maybe up to the immigration. Maybe it will even only be 1,900 THB like with all other visa. Cannot say at this point.
Or they might adidtionally tell you to put a certain amount of bills in your passport before handing it over again for stamping you in "one last time". Having a Thai girlfriend changes nothing about one being refused eventually if living solely on tourist visa or visa exemptions.
I would like to have clarification on tax-related implications: How is the tax being handled? Will foreign income be taxable in Thailand (cause I have read articles that they will not while on a DTV, but have not found anything official about that)? Will foreign income be excluded from taxation (like with the royal decree in case of the LTR)? If not, why would people working for foreign companies on a LTR be exempt from tax, while people doing the same on a DTV won't? If foreign income is taxable while on the DTV: How to apply for a tax id in Thailand (as it currently requires a work permit or at least income from within Thailand)?
I had a very similar issue with the LTR. Although meeting all other requirements and working for publicly listed company, I was denied as I wasn’t a direct employee but routing my money through a wholly owned corporation for tax optimization.
It is what it is (for now), so I don't have to bet. All current communication including the legal wording in the Royal Gazette supports this. Will they keep it that way or around for long - we will see. I kind of doubt it. On the one hand, they were cracking down on people abusing ED visa, and now they are basically letting everybody who can show 500k THB in any bank account stay for 5 years (with a few legal border bounces). Amazing Thailand.