if you don't think you'll add more amps i would use the four gauge for later use. but if not 8awg should be good enough for you.

the clear plastic case in the engine bay was the fuse holder. the black box coming off the speaker was a line out converter. basicly its for when you don't have rca outs on your stereo.

yes usually the switch your talking about is just a lil toggle switch that is hook into the remote wire so you can turn it on or off. i only install those on car that people want to have that annoying loud bass so they can turn it on if a cop drives by. i say just don't be that butthole and turn down your stereo.