All good points that about have it covered, and there's a couple of things I wanna add. After you figure out your nicotine level, make sure to have juice on hand, it doesn't matter if you're doing cartomizers or a three-piece unit. Even if you prefer to use cartomizers and don't intend on refilling, nothing's more frustrating having made the switch to find out that your carts have been backordered so you'll have to go back to analogs for a few days or weeks. Think of that stash as your go-to juice; it may not be absolutely mind-blowing in flavor, but it's there to get you by.
Another thing is to get an extra battery. Most starter kits I've seen come with two. Two's good; I can vape all day on that. But I recently blew my first battery (go me!) and I'm having to hobble along on one until Smoketip sends my replacement. (Or until my extra I ordered from vapor4life comes in. I'm not picky.) That third one handy lets you keep on trucking while one's getting repaired.
Other things you may wanna consider since you're switching off of analogs is to not try to change too much at once. Do your vaping when you normally would smoke, and where you normally would. (Treat yourself with where you normally wouldn't; in my case I can now vape in my car and in the house--I didn't want either to smell like an ashtray) Also, these tend to dry you out a bit, so make sure to get more fluids--dry mouth seems to kill flavor IMO. Get a case that's about the size of a pack of smokes that will handle your gear for a day or two. I used to catch myself feeling for a pack of smokes and panicking when they weren't there.
Hmm....there's also this to consider. Juice is normally sold with a PG/VG ratio listed. If your vapes are a bit too harsh on your throat, try getting juice with more VG in it. Tends to be a little sweeter, a lot smoother, but it seems to dilute the flavor. If it's too smooth and you need something with a stronger flavor and a bit more kick (throat hit), then opt for something with more PG in it.
That's about all I've got to say about that...happy vaping!