I tend to bring my own cigars, but you can get them in the same shop that has duty free liquor and sundries. They are kept in a humidified wall display. Old doesn't matter, because often older is better anyway. I prefer to smoke on the Meridian aft deck. It's usually less crowded, there are cigar-specific ashtrays, it has couches and tables and there is shade. Deck 4's smoking area is basically a standing-room-only hallway with wall ashtrays, and Deck 13 is packed with cigarette smokers as well as being out in the direct sun and wind.
Yes, you can bring a lighter on board. I need to pick up another cigar lighter. I'm primarily a pipe smoker, so my lighters don't tend to have the horsepower necessary to light a cigar with a breeze blowing.
When is your Fantasy trip? I'm looking for fellow cigar smokers and whiskey/whisky drinkers to hang with on our trip. Smoking a cigar by yourself can be boring unless you have a good book and a full flask.