I get a lot of my juice from Gourmet Vapor. They have a lot of different tobacco "flavors", so you might want to check there. (While they're not an ECF registered supplier, they have been reliable and fast, in my experience.) I'm sure you'll get lots of other recommendations as well.
The resistance of the coil will determine how high a voltage you use to get the vape you like. Higher value resistance requires higher voltage to get the same watts of power. Lower values heat up quicker, and may produce a warmer feel to the vapor, and vice versa.
Shaking a clearo / vivi isn't needed, although rolling it may be, when the liquid gets low. Hold the entire device at a shallow angle, almost parallel to the floor, and just roll the battery back and forth in your fingers to make sure the wicks are wet. Some top coil devices may still use short wicks, and this rolling is especially important with them. The Vivis and most of the newer "stardust" styles have longer wicks, so its less of an issue.
A general rule of thumb is that each 100ma of battery is very roughly equal to 1 hour of vaping. Of course, all our styles vary, so take this with a big grain of salt! So your 650s may give about 6 1/5 hours of vaping. But best for the long term life of the battery if you recharge before it's dead.
And try here to see if there is a shop close to you. While it may not be totally complete, it's a good starting point.
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