ok to answer your questions in sequence..
1. the guitar package should give you everything you need to start playing. the amplifier is good enough for home use. no need to change any parts of the guitar, unless you have too much money in your hands. i believe that you should buy a guitar because you like it just off the rack, not buy with the intention to change parts.. unless you specifically want to DIY.
2. learning chords, and how to play the guitar in general.. you can learn from your friends or look for a guitar coach/teacher even. either that or you can learn yourself from online sources.
3. humbuckers are a type of pickup. pickups are the things you see below your guitar strings and fixed on the body of the guitar. their function is to pick up the vibration of the guitar strings and produce a sound, which is why they're called "pickups".
now a useful link..
Guitar Lessons for Beginners Archive - Free Guitar Lessons Online - Acoustic and Electric Guitar Lessons
also includes recommendations on how to choose a guitar, and the different parts of a guitar.
enjoy.