You do not need a mounting kit. I made the mistake of buying it and I didn't use one part from the kit. I would suggest buying the wiring harness.
Also, don't buy from Crutchfield. They are way too expensive.
Also if you haven't seen it yet, check out the tutorial:
http://www.nicoclub.com/articles.php?id=227206
That helped me out a lot. Like the tutorial says, don't unplug the airbag light...there's one little screw that holds the light to the dash. The tutorial tells you how to cut and splice the existing wire, but I would suggest buying the harness.