1.If i just used a carputer+touchscreen LCD Would i need a HU or just amps+speakers?
you will need some sort of amp-- some use a HU, others(like me) just use amps
2.Amplifiers need a negative and positive input if im not mistaken (yes that was a question)
on a headphone jack(or computer speaker output), the stereo signal shares the negative wire connection-- in most audio systems, the negative of the signal is a combined shield-- ie. all the outside parts of the rca's of one amp are wired together.
3.What would be a sufficent wattage for speakers, amps and subs (im a 19 year old guy with a love for bass )
there is no right answer for this. it is all personal preferance.
4.i am planning to fabricate/install the LCD and laptop DVD Drive into the dash with the carputer behind it.......would this be awfully difficult?
it depends on your fabrication skills. also, it depends on if there is enough room behind the dash for the install. i had originally planned on doing that also, and checked that the MB would fit, but there was not enough room to connect the cables...