to have a proper system you need

1 Deck for sound
1 or more subs for bass
1 or more amps for subs
1 set component speakers for optimum sound
1 amp for component speakers for optimum sound

Other optional pieces is a good line driver to bump up the voltage to the amp
You want a deck with at least pre-outs for the front and a sub
You want the pre-outs to be at least 4v if not higher
Remote wire from deck can be 14g
Power wire from battery to amp for subs should be at least 4g with as many strands as possible (conducts more electricity)
Ground wire should be at least 2g