About to install sub/box/amp, quesitons....

I asked a few car audio shops what it would take to get it running. From what I've found, I need a converter that plugs into the factory HU to get it running. Shop said this is about $20. I also need an amp wiring kit, about $45. I know I could have picked up this stuff online for 1/2 that, but it's too late now.
I'm thinking of buying the parts and tackling this with a friend to save some cash and get some satisfaction. I've also read that it's really not very hard to install this into C5s.
Question time:
1) How do I get to the back of the HU to plug in the connector?
2) Is it easy to move the changer over to one of the side compartments? I need to do this to fit the box.
3) I know I need to run the cable from the battery through the rubber grommet in the firewall. WD40 can help, sound accurate?
4) What rear carpet/panels do I need to remove to run the wires to the changer, amp, and sub box?
5) Where do I run the cables that go through the firewall? And what side panels do I need to pull to get to the carpet?
6) Can I mount my amp, it's pretty small, in one of the side compartments?
7) Are there some install pages with detailed pics to do this?
Thanks for any help!





