Replacing speakers, headunit, and adding a sub questions

Title pretty much says it all, I'm probably going to pick up my cousins 12" solo baric for a decent price, and I'm going to put all new pioneer door speakers and pioneer speakers for the back in. I'm also probably going to run either of the following two head units:
http://www.bestbuy.com/site/olspage...t&productCategoryId=cat03066&id=1099388424889
http://www.bestbuy.com/site/olspage.jsp?skuId=6981475&type=product&cmp=++&id=1099388424999

Me and my dad will be doing the installation ourself. I've heard that I'm going to have to run a new wiring harness or hack up the one I got. I'll just run a new harness, even if it is more troublesome. I assume my lx has 6 speakers since it has what appears to be openings near the top of the dash for speakers. It doesn't have the equalizer though, if that makes a difference.

For the sub it's going to be a 12" solobaric, probably in a truck box. I'll probably put it up against my back seat in the hatch. I don't want to drill holes in my car so I'll probably lay a sheet of plywood down in the back and bolt the box to it unless you guys have a better idea which would be cool.

For the amp, for the time being I got a decent one from my friend who upgraded his after christmas so I'll probably use it for the time being. As for the possibility of running an amp for the door/backseat speakers, would it be worth it money and time wise? Or would it sound just as good running from the head unit.

Thanks!

I got a decent 4 channel JVC amp that my friend gave me that I may use for the f/r speakers since it's not a lot of wattage. I'm sure it would be a plenty for them speakers, then pick up an alright amp for the sub. I thought about picking up another box , but I still have to figure out how to mount it.

I'd definetly not hacking up the wiring. I just don't do that, and I'll probably return it to stock one day. I'll probably just either run power from the radio or this amp, my friend wants the amp so I may just sell it to him and run power from the radio, then an amp to a 12 in the back. I really don't run all new wiring either, and I'm just looking for a decent sounding system, nothing to really impress anyone with.