Advantages to components:
1) Crossovers are better.
2) Each speaker plays the frequencies it was designed to.
3) Theres no 1" hole in the center of your midbass driver
4) More flexibility in tweeter placement depending on how bright you want your speakers to sound.

IMO, you don't HAVE to amp the components, but it does make them sound a lot nicer. I would say a clean 50x4 is all you need, and if you are on a budget, just leave the 6x9's running off the headunit and get a small 50x2 for the fronts.