While I would love to go through all of the instructions for this, I would seriously recommend getting it installed at a bestbuy or a proper car audio shop.
Punching a hole in the airwall also requires the proper use of a rubber grommet and some anti-rust proofing.
They will have the proper tools at most shops to do this, plus they'll be liable for a screw-up.
as for splicing in, if your amp supports a high level input signal, you shoudl splice as close to where your amp is as possible, but the better thing to do is have an installer do it, and purchase a line converter to do this and a long set of RCAs. This way your splicing wires do not have signal loss and degredation running from the doors or behind the HU to the amp.
D