Thai banks don't know what a DTV is nor are they able to "classify" it. Unfortunately, it's difficult to open a bank account regardless of what visa you have unless it's a non-O or non-B and accompanied by either a work permit or work permit application.
Retirement visa holders can find it difficult to open bank accounts too, because they don't hold a work permit.
You'll need to visit a head office branch and/or use an agent.
You can even use your credit or debit card to pay for the subway in Bangkok. Not sure about the BTS - possibly as well (needs to be double checked, as I haven't used the system in years, so I'm not sure).
Absolutely no problem. All visas are fine to use with just a one way ticket. The only visa for which I'd recommend having an onward ticket (though it might not get asked for) is if you possess a valid single entry tourist visa.
How far back do they want you to go? Just show all the previous visas issued over the past year or two but don't bother with any visas issued in previous passports.
Nope, because to qualify for permanent residency, only a non-O or non-B that are extensions of stay (not the visas you get outside of the country) plus employment in Thailand are acceptable (meaning you also need to hold a Thai work permit).
You don't qualify for permanent residency if you're on a laborer visa (for Vietnamese, Cambodian, Burmese and Cambodian nationals), a retirement visa, tourist visa, any visa issued abroad (including the DTV), or even the LTR or elite/privilege visas.
A smart visa might qualify (not sure) but otherwise, only non-O and non-B extensions of stay...3 consecutive ones plus a minimum income of 80,000 Baht per month (40,000 if married to a Thai) for a minimum of 36 consecutive months. If any months are missing, you start from scratch.
The tax thing is still unclear and not yet enforced (it might never be, or it might only be enforced in a few years...anyone's guess right now). The point is, immigration is most definitely not interested in it. It would be hilarious if they asked for tax proof while you're standing at a land border coming back in. If that ever happens, foreigners will stop coming to Thailand so I don't think that's something to worry about.
Totally agree. At this point, I wouldn't worry about it and not take any action. Unless enforced, at which point you can decide how to deal with it. At this stage, nothing will happen.