Speaker Installation Question and Amp..

Alright so I'm driving a 1997 Pontiac Bonneville 40th Anniversary Ed (two grilles each door)

Anyways, I just recently bought all this to upgrade from my all factory system:

Headunit:

http://www.amazon.com/gp/product/B0074A5KNG/ref=oh_o02_s00_i00_details

Rear 6x9 Speakers:

http://www.amazon.com/gp/product/B002CIU78I/ref=oh_o01_s00_i00_details

Front 5.25 Speakers:

http://www.amazon.com/gp/product/B002BZE36E/ref=oh_o01_s00_i01_details

along with wiring harness for the headunit and installation kit it should all come in this week.

First, Do I need a speaker adapters for the installation or is it just all plug n play? If so, could someone lead me in the direction of where to find these? Anyways, I have a question about amplifiers and subwoofers. I don't understand how if I get a 4 channel AMP for my speakers, how the front only wants 45watts RMS but the rear wants 100watts RMS, how the amp can supply both without either 1. not giving enough power to the rear and 2. giving too much power to the front.

Are there dials for each channel on how many W to give? I'm a complete noob. Also, I'll probably buy some subs down the line and I understand that would need a different amp too.

Thanks!