It probably varies a lot for people, but for me the hand to mouth habit is the hardest to break. I'm down to 2mg nic, and don't see a problem going to 0 nic, but still enjoy vaping, and will continue to vape even if I go to 0 nic.
I have read a few places that nicotine in small doses can be beneficial to brain health, so maybe I'll just stick to 2mg.