Regarding 510 connectors:
'Flashlights' with 510 connectors are very likely to fall into the category of ENDS, and that does mean that they would not be legal for sale in this country.
However, FT selling them would still be legal, and my guess is that a package labeled 'flashlight' is FAR more likely to make it through customs than one labled 'e cigarette'.
Regarding mail order:
One simple amendment to the PACT Act (google it) and its game over.
That amendment could come at any time, and would affect all states.
I live in NYS, so I'm stocking up as fast as I possibly can, but don't think that just because you live in a free state that it can't happen to you.
I've only been vaping just over a month, and I've gone from not really knowing anything about vaping to using mech mods and building my own coils.
I have built five coils so far, and all of them are still working perfectly.
I have compiled a list of gear to buy, and I'm getting five identical tanks, five identical mech mods, many, many spare parts, and a liter of nicotine for around $250.
It's not difficult and it's not even all that expensive - $250 is less than most of us spent on cigarettes per month.
If none of this comes to pass (and that is looking increasingly unlikely) then I will still have everything I bought, and will still be able to use it, so it is impossible to lose either way.
If the regs stick, I will be REALLY happy that I took precautions.
No matter what happens over the next couple of years, you can be sure that vaping will never be as cheap as it is right now.