Reacting on your title: Arduino can be a hobby, a profession and even an addiction 
A nice free reader - http://www.earthshineelectronics.com/files/ASKManualRev4.pdf - and of course the tutorial section - http://www.arduino.cc/en/Tutorial/HomePage - is a good place to start.
Every starterkit will do, be aware that you will not do all experiments and you will have a components-heap somewhere.