I have a 2007 Dodge Charger R/T v8 5.7L Hemi, i installed Kenwood DDX 7029 head unit and would like to know the following:

How many speakers does my car have by default (i'm kinda noob for this whole sound systems gig)
What speakers from Kenwood will fit my car as OEM replacement without modifications
If i install a subwoofer, do i need an amp between the head unit and the sub? and what is the sub i should use

the following is the audio cap for the head unit
max power (front&rear): 50w x 4
full bandwidth pow. (front&rear) (PWR DIN45324,+B=14.4v): 30w x 4
preout level (V): 2v/10k?
preout impedance: 600?
speaker impedance: 4 - 8?
tone action

bass: 100 Hz±8 dB
Mid: 1 kHz±8 dB
treb: 10 kHz±8 dB
operation voltg: 14.4v (11 - 16V allowable)
curr consumption: 15 A