A few points:
1. Someone said nicotine wasn't that addictive, and I want to say that's irresponsible crazy talk in the nicest way possible. I can't post links, but a quick google of "nicotine vs ...... addiction" will show lovely charts. Nicotine is crazy addictive.
2. You seem like an addict who isn't fully able to quit, and is hiding it. Totally normal, I was there, but you have to decide what your goals are. Do you want to actually quit, or do you want to have your addiction be more manageable?
3. If you are hiding your smokes and maybe having one or two a day, going to 12mg will basically take care of everything, but also increase your addiction. Instead of going and taking a few puffs to let the craving pass to where it's manageable and you can go hang out with people and not smell like smokes, your body will slowly get used to (and want) a higher nicotine level.
Cigarettes are absolutely horrible for you, not really for the cancer (less people get cancer than you'd think) but for the damage it does to everything else. Nicotine is much safter, with research showing it basically increases blood pressure/pulse/hypertension, and other types showing it inhibiting bone growth and such. So ecigs are a huge win if you need the nicotine compared to smoking, but nicotine isn't a vitamin -- and there's lots we don't know about vaporing flavorings and such. With nicotine e-cigs, you are *substituting* one addiction for another, one that is hopefully healthier and causes less impact on your life.
I'd consider getting 6mg *and* 0mg. When you find yourself getting fidgety and terrible to be around, sneak away and have some puffs of the 6mg. But when you're just experimenting and enjoying the taste and finding it relaxing, use 0mg. Don't invest in a bunch of equipment, it makes it easier for you to then decide you're over the whole thing & lose interest.
*gives the horns*