Theta Ridge (www.thetaridgecoffee.com) will split bags all the way down to a single pound (or anywhere in between), if you'd like. You can also find 1, 5 and 50 pound bags through ProCoffee (www.procoffee.com). I've purchased from both and have had good experiences with both companies.
The rest of the folks have given you great input about how long the green beans will last in storage.
Just remember one major thing regarding this. You are about the 32nd person to have touched this coffee. A lot of barista's forget this major fact. So it's so important that you look into every bit of detail that you possibly can to ensure a good cup.
What everyone has said is all very true. however they are forgetting a very crucial task. Storage of your coffee after you have roasted it. The green bean is extremly resiliant, and can withstand a bit of a beating. However once you have roasted the coffee, looking after it becomes even more crucial. When do you bag it? How long do you let it de-gas before bagging? How do you properly de-gas the coffee? These are some major things you need to take into account. I know of some people that will do a roast, and for a month, test the coffee everyday of the month to see how it de-gasses. when is it's optimal bagging time. You might find some coffee's are better left for 2-3weeks before bagging, and some a couple of days. You need to find out for yourself what works best for you.
So yes, looking after the green bean is important. However, looking after the roasted coffee is even more!