Stereo & Electronics - Newbie needs some clarification...

I've got a '98 Ws6 which I'm planning on replacing the HU in this weekend since I have some time off from work. I'm thinking of the Pioneer DEH-P470MP HU: http://www.pioneerelectronics.com/pna/product/detail/0,,2076_4041_150519112,00.html Nothing too fancy...should be all I need. My main question is where can I get the parts I need to install this. I need:

40-GM10 - GM factory antenna adapter for aftermarket head unit
99-3009 - Camaro 93-96/Firebird 1993 and UP dash kit
70-1858 Pro Wire harness for 1993-02

The first part sure looks like a GM part number to me. I guess that means a trip to the dealer? I have this antenna adapter I used looong ago, but it was for another vehicle. I'm guessing this won't work? http://www.geocities.com/jsramair/AA.jpg - copy and paste

The mounting kit...is that the part number for the Metra kit? If so, where can I buy one?
Same question for the wiring harness. I've read that you can get one at Wal-Mart or Best Buy, but I don't know if there is a specific type I need.

Also, I'm going to get a PAC SWI-X for the steering wheel controls. Where is the cheapest place to get one? Do local stores/audio shops have them?

Sometime after the HU install, I'll be getting new speakers up front since one of mine is busted and I 'might' get some for the rear. Depending on how all this sounds, I may get an amp to power the mid-range speakers. I currently have two old 10" Orion Cobalts powered by a RF amp. The subs I'm completely satisfied with.

So who can tell me where to get all the accessories? Thanks.

order from crutchfield and you get that stuff for free, they also carry the PAC, plus if your gonna spend that much, you get free shipping too.

I'd be too impatient to wait for shipping. I'm usually the type who heads over to Best Buy.

That's the thing...I'll be doing it this weekend (maybe as soon as Thursday) and I don't want to spend a ton on 2 day shipping, if that's even an option.

Also, I won't have a problem using my factory 12 disc cd changer, will I?

No, you won't be able to use the factory changer with an aftermarket head unit.

So where can I get the mounting kit, wiring harness, antenna adapter and PAC SWI-X? I guess most electronics stores/audio shops have them?

Most stores will have the kit, harness, and antenna adapter but you might have to go online for the PAC adapter (depending on how well stocked your local store is).