The power you have is determined by your head unit, the one you're looking at is 50W x 4 which means it can supply 4 speakers, 50W each. A 4 way speaker for example breaks the sound into 4 ranges by frequency with the higher ones going to the tweeter, the lower ones going to the woofer, with the remaining middle going to 2 mid ranges. From what I know the amount of drivers(ways) isn't directly related to sound quality, listen to the speaker and see what sounds best to you. I don't think you'd need an additional amp unless you wanted to go with a sub. The stereo should come with a harness that plugs into the back of the stereo, you should be able to buy a harness that fits into the harness that you will remove from your stock stereo(factory wiring), wire the 2 together, there should be directions telling what color wire is what. Its just a Toyota to Pioneer adaptor. I swapped out the stock sound system for a Pioneer DEH6700 with four 6.5" Memphis 3-way rounds. Its sounds great, no matter how high I turn up the volume it stays clear and no bass muffling. I had to make adapters beacuse the hole pattern on the speakers didn't match the stock mounting holes.