How many you need, at least at this point, matters less than how wide of a range you have available. Even then, the top end -- tallest gear, fastest gear, whatever -- is likely to be plenty fast for anything you'll do, while the low end is what you need make a decision about -- how low do you want to go.
It's better to have a bottom gear that's short enough to crank up that steep hill at the end of your ride than it is to have to walk. But, you might not need a stump-puller gear after all, whether it's because that last hill isn't very steep, or you're pretty good at climbing, etc etc.
So, then, decide. If you have a triple crank, but never use the granny ring for anything, you don't need it. If you
do use the granny ring, but you still aren't using the biggest 3 or 4 cogs in the cassette, you probably don't really
need the granny ring, either, because you'd get the same gear ratios by using the middle chainring and biggest cogs.
My first road bike came with a triple, and I never used the granny ring for anything. I replaced it with a double.
Take some time and fiddle with Sheldon Brown's gear calculator. In particular, look at how the gear combos overlap -- you might have a choice of 30 ratios on a triple, but many of them will be redundant.
http://www.sheldonbrown.com/gears/