just get it professionally done...
I have installed 4 headunits on 4 different cars, and my 280Z was unattemptable for me. To many wires, too many chances for mistakes.
Lets the professional's do it..
You may also have to re-wire your speakers or get harness' for them and make a custom mounting bracket and holder, so your pioneer won't come straight out when a theif grabs it, just in case... so you make it so tricky they don't have enough time and bail out.