Speaking of nic level - I don't like the fact that you can't determine the level of nic in a 'real' cigarette. I tried to do that, but could never find anything tangible/reliable. So, I took a stab at 12 mg/ml - have heard here that I should go to 18, have heard othermembers say it's not necessary??? If my current set up works for me (vapor/usage/handling), and I still am terribly drawn to cigarettes, I will probably up the nic level to see if that works better.
the amount of nicotine you need depends on what device your using and your consumption level of ejuice, coupled with how much you used to smoke.
most heavy smokers (2 packs per day or so) do best on around 80-100 mg of nicotine per day when quitting. (of course, if you werent a heavy smoker you can cut that in half or less, depending on how much you smoked)
from there you have to look at what your daily consumption is, which varies with power level and atomizer you use.
for example if your consumption is 5 ml of ejuice per day, you might like to start at 20mg ejuice, and see how you do. if it's too much for you, lower your nicotine level to 12mg, if it's not enough, try 25 mg.
if your using a pod mod that's extremely low nicotine consumption, you'd like to try the nicotine salts 48mg, if that's too high you can bump it down to 35..
if your on a sub ohm device that has a higher consumption level, you'll want to start at 6mg and if that's not enough then bump it to 9mg..
so device and power levels make a difference, but it's easy enough to figure out.