With a constant voltage battery, the only way to change the wattage (how hot the coils get) is to change the resistance, due to Ohm's Law. But with a variable battery, you can accomplish the same thing by adjusting the power, so the resistance of the coil doesn't matter as much.
More voltage means more watts (assuming a constant resistance), and more watts means a hotter coil. I'm not sure what that really mean by less resistance means more voltage, unless you mean less voltage needed to get the same wattage. Play around with an Ohm's Law Calculator, maybe seeing all the numbers and how they relate to each other might help.
Start at a low setting and work your way up until you find what you like. A lot of it is personal preference, and also different juices can have different sweet spots.
I think the coils will last longer at lower wattages, but I'm not sure how much of a difference it'll make. Might not be enough to be worth keeping your wattage lower than you'd like. http://www.aspirenautilus.com/