You need to surf some of the supplier websites. Also, update your profile to show a location, at least country, so we will know which sites apply to you.
Some people use the liquid to refill cartridges. Some put a couple of drops directly down the atomizer and don't use cartridges at all.
Syringes are handy for mixing and refilling cartrdiges, but not totally necessary I guess.
Having not smoked regular cigarettes in over two weeks now, it's hard for me to truly tell you how much liquid equals how many cigs. I think my e-cig habits are quite different from my regular smoking habits. I don't go outside and stand there smoking a whole cig. I grab this thing and take a few puffs whenever I want, so it changes things. I can tell you that I smoked approx. 1 1/2 packs per day and now that I'm totally on the e-cig, I'm using about 1.5 ml. of liquid a day.
Hope that helps!