There's no such thing as a set or appropriate voltage. The best advice for voltage and coils would be, add two volts to the value of the resistance, and you can turn it up or down to find that sweet spot..so 3.8 Volts. Since it is a clearomizer, I would probably be turning it down, but you never know. A lot of flavors will need a different voltage level. Just find the one that works for you. You'll know if it's too high or low.
When you get into rebuilding your heads, this question will have a variety of more appropriate answers. Not only will the flavor have to be taken into consideration with the resistance, but you'll need to adjust it accordingly for the wick material you decide to use.