I am going to hook up my amps in my CRX, but I rear mounted my Bat. Now should I run the Neg. cable directly to the Bat. or to the cars metal body/frame? Or does it matter?

Also I dont have a four channel amp, but I have 3 small 2 channel amps, 1 amp will be for the 2 small subs, another amp for the small rear door speakers and the last amp for the small front door speakers, im on a tight budget, so does it sound like an ok setup?