As a newbie, i wondering what to buy after i bought the starter box??

There is no one-size-fits-all answer. It depends on what Factions and Strategies you're interested in playing, how tournament competitive you want to be, and how many other new players there are in your area.

With these things in mind, I suggest you go read

http://boardgamegeek.com/thread/1090522/a-beginners-guide-to-expanding-netrunner