What you want to do is fairly clearcut, and what you need to do is start with a couple of 510 atomizers and a 510 usb passthrough that runs at 5volts. As far as I can see, that is exactly what you think you want at this point. It is the cheapest way for you to get started. And I think you should only think about trying 6v if the 5v somehow isn't enough for you.