Don't be too worried about dropping your nic level. You can take it down when you feel ready. You can give anything a try whenever you feel ready. And if it doesn't do it for you, there's no shame in going back up. I've found when dropping nicotine, you might feel a little dissatisfied for the first couple of days, but you'll get used to it.
But like I said, I wouldn't be super worried about it. The whole point is to stay of cigarettes. If it takes staying at 18mg for however long, so be it. Personally I've bounced around all sorts of nic levels through the entire time I've been vaping. Started at 16mg (I know. It's not standard, but that's what the company I started with was making). Ended up at 18mg not long after that. This was back when I was using something like a cig-a-like. Got a VV mod (one of the early ones. 6 volt capability was a big thing at the time) after that and dropped to 12mg. Then 6. Broke the VV, broke a couple VVs actually. They were pretty fragile back then; back to the cig-a-likes and back to 18mg. Then I went to mech mods and dropped to 6. Ditched the mech mods for simplicity, a couple Itaste sticks. Back up to 12, and then 18. Bounced around 12, and 18 for a while, and was at 6 for a short period of time. Now I have a Coolfire IV and a Dripbox. I usually use between 3 and 6 depending on what sort of build I have, and time of day. Higher in the morning and around the afternoon hump, lower for maintenance and right before bed.
Unless you have an unhealthy cardiovascular system, it shouldn't be much of a worry for you. Just go as your body will let you. It's not a race.