House juices aside, most B&Ms/online vendors wouldn't fall into these categories. Would they? If all they do is sell an already packaged product, it would be similar to any gas station selling actual tobacco products. Provape, Volcano, and Vaporshark are screwed. At least in the near-term. I would imagine that some kind of trade negotiation/tariffs would be placed on foreign imports. Hopefully they won't be outright banned until big brother deems them safe. I've put on my tinfoil hat and bought a few new mods, tanks, DIY supplies, etc. Should be good for a while. Still looking for a tube mod just for giggles.
Yes, mixing and selling e-juice is the big one to make our vendors a manufacturer. And as you said, those companies making and selling mods (ect, Provape) will need to file their paperwork. Technically if they purchase factory coils in packages of 5 from China (as many of them do) and take them apart to sell as singles (as many do) that also would make them a manufacturer. As long as whatever finished product they purchase (from US or Imported) they turn around and sell "exactly" as they bought it they don't have to file as a manufacturer.