I have been vaping since July 2010. I started with some 36mg juices. I now have a variety from 12-36mg. If I am know I am not going to be able to vape frequently, I take the higher mg with me. At home I use whatever I happen to grab. When I was smoking analogs, I smoked Misty menthol light 120's. But even though they were 'light", I took long drags, and smoked to the ..... I know I could finish a 120 cig before some of my friends would finish their regular cigs.
I do believe I am getting more nic now because the frequency of use is greater. I never smoked in the house, but now I vape in the house and even in bed. I have never gotten light headed, but if I feel a bit queasy, just drinking some water helps.
I think the nicotine level you need depends on how you used your analogs.
I am far from being an expert, the comments above are just from personal experience and observations.