Few words of advice . . .
Stay away from Sony decks; they used to make good stuff in the early and mid 90's, particularly their Mobile ES line. But with the advent of a lot of their "Xplod" stuff, it really started to suck. This year's models don't look as bad as the past few years, but for the money, I'd get an Alpine, Pioneer, or if you're feeling particularly rich, an Eclipse or Nakamichi head unit. You can't go wrong there.
With regard to speakers, I'm not a fan of 3-ways. A good 2-way will beat most 3-ways, especially considering the "supertweeters" most have produce sound that most head units aren't capable of reproducing, and even if they were, the sounds would be out of the range of the majority of people's hearing capabilities. I'm not sure what the Kappas would run you, but I would get a set of components before them if the price is right . . . it's the next step I'm taking.
Oh, and if you need more information, Car Audio Forum is a great place to go . . .
http://www.caraudioforum.com/