Well, as far as the radio goes - Pioneer is a good brand. If the unit is in good working order, you should be alright with it. It *is* a model from last year though, so there likely won't be any warranty on it anymore. The 8500 model is basically what is now the 8600 model, but with the dual-face plate of the 9600 model.
From what I've read the sound quality did improve a lot on the current model year, but then again, the current model of that specific radio (which would be the 8600), will cost you at least $320 (that's the cheapers I've found it for online) plus shipping. So it's definitely cheaper.
As far as the install kits go, lots of places carry them... I got my bezel at the local cartoys for about $15, and the wiring harness for about the same ($15-ish) at Circuit City.
Volant CAI, SVT Snorkle, Focus Central 65mm TB, Ford Racing Shorty Header, Random Technologies High-flow Cat, Trubendz 2.5" SS Flexpipe, Trubendz 2.5" SS Exhaust w/ Magnaflow Muffler
Pioneer DEH-P8600MP, JL 10W3v2 (in JL Audio Stealthbox), JL Audio e4300, Alpine MRP-M350, 4x Pioneer TS-A6880R
Speedhut reverse glow gauges, FC Shorty antenna (Red)