What I wish I knew, before I started:
1- It's really hard to find a tobacco flavor similar to what you're using; all juices will taste different to everyone, so get a sampler. You'll soon realize that your choice of flavors is now infinite. Start with a caramel/tobacco, and you might start considering a fruit flavor. Some vendor's juices need to sit, for their flavors to settle. Good vendors will let them steep as needed, before selling them to you. Steeping time can be in the order of weeks. Some e-liquid flavors are just unstable over time (rare).
2- Start out with more nicotine than you normally use now, but be ready to switch back, quickly. I used to smoke ultra lights, and I assumed that 6 mg/mL would be the same, but I soon hit nicotine withdrawal. I had to switch to 12 mg/mL, but after 3 weeks, I'm ready to take it back down to 6. It's OK to order nicotine-free flavors; they might taste a little different, but will hold you over, if you've had too much nicotine. Your heart starts to race if you get too much nicotine.
3- You must absolutely know what type of threading is on any e-cig you buy. Slim ones should be 808D-1 (not 808D-2). Larger ones should be eGo or vGo. (eGo is a 510 thread, on top of a larger thread, while vGo is 808D-1 on top of the same larger thread, but eGo and vGo are not interchangeable). eGo is far more popular, if you're looking to mix vendors in the future (most, but not all, are interchangeable). I chose vGo, because I wanted the backwards compatibility to 808D-1, without an adapter.
4- Do your research here on ECF, before buying a new e-cig. If you make a wise choice at the beginning, you won't end up purchasing a large variety of hardware, negating your savings. Ask questions; there's plenty of good, legitimate advice going around here; there's a lot of bad sponsored reviews out there on the web.
5- it's ok to start with a slim cigarette, it's even preferable. Cartomizers are a great way to start. While cartomizers can be refillable, it's a bother, and you can achieve significant savings by switching to a good tank system, especially if the atomizer (coil) is replaceable, and it's far easier to refill.
My first e-cig kit was an 808D-2, and their cartos were $3 each. I quickly found 808D-1 for $2 each, and bought adapters to use them, but I quickly moved on to a tank, where the juice is less than $1 per mL.
I like to know just how much nicotine I'm going through, something you can't do with cartomizers, unless you refill them yourself.
6- The ultimate system will have a battery with replaceable cells. It will have a VV and/or VW circuit (Variable Voltage and/or Variable Wattage), so you can set the voltage or even better the wattage (power) to vaporize your e-liquid. They might be more expensive to start with, but if you're going to be a vaper for a while (as most of us will), it'll pay off quickly. Variable voltage is fine by itself; variable wattage is fancier, and works independently of the resistance of your coil. Batteries don't last forever (1'000 recharges?), and it's a lot cheaper to replace a cell, than the whole battery unit. No you can't use a multimeter to measure the Ohm (electrical resistance) of a coil; the Ohm rating is different under load.
I'm using an unregulated Halo Triton batt and tank right now. While I do notice the drop in power as the battery discharges, it doesn't bother me, yet. Fancier systems are for fancier tastes.
I am beginning to wonder if the e-cigarettes should have been called something else altogether from the start.
