Well, the amount of charcoal you are going to start with really depends on what you are trying to cook and how much. Say a couple of steaks or burgers for you and the wife, doesn't take a whole lot of charcoal for that. But if you're cookin' up steaks, brats, hotdogs and burgers for a big family gathering, then for sure a big ol' chimney full, and maybe then some. Also depends some on what you may be cooking specifically and how you want that cooked. If you're grilling a big thick steak and want a real good char on it, you may want more coals to get that really hot hot base going. On the other hand, a trout or salmon filet, you may want to be less aggressive with the heat, therefore not so much charcoal needed.
And then of coarse, you can get into the whole two and three zone cooking methods, whole nother technique, Check out the Weber website as well, I think they have a bunch of tips and tricks there too.
It will come with practice, just adjust your technique to your liking as you go and have some fun with it. Gives you a good excuse to grill and Q too, "need the practice".
Weber Performer with rotisserie ring, 22.5OTS, Maverick 732, Weber Smokey Joe,PBC Smokenator/Hoovergrill, variety of microbrews, Gin and tonic, variety of lighters.