One thing to keep in mind is that Marlboros have lots of stuff in them that vaping won't replace... it's what makes a Marlboro a Marlboro rather than a Winston. I'd drink lots of fluids to flush the residual toxins out. As previously suggested, mixing your fluids to get 18 mg isn't a bad idea either. You're on the right track.
Marlboro was one of, if not the first brand of cigarettes that was guilty for adding ammonia. Ammonia gives a bit harsher taste, but it also slows down the breakdown of nicotine. Back in the 1960's, RJ Reynolds was trying to find out how Phillip Morrison's Marlboro brand was so popular. They discovered that RJ Reynolds was adding ammonia to raise the PH balance. Although ammonia occurs naturally in a tobacco leaf, some ammonia is added to reconstitute tobacco. It is also part of the process in making the paper for cigarettes... the stalks and stems of the tobacco are used to make the paper for the cigarette.
But the end result was... Marlboro tasted like a Marlboro largely due to the ammonia.
If you want to read up... there is a long, but interesting article you should read about the history of ammonia in cigarettes. The SECRET and SOUL of Marlboro: Phillip Morris and the Origins, Spread, and Denial of Nicotine Freebasing