Jaycar gear is all good stuff!
when you buy a head unit check out jb first, and remember they will always bargain. i got my head unit for $430, and the marked price was $569 (aparrently marked down)
the unit i got was a Pioneer DEH-P5550MP
which plays mp3s as well, which makes a stacker useless...
With speakers, if you are going to get a sub its not worth doing anything extra special for your shelf or fronts. 6" rounds (good ones) will do the job with a sub to back them up.
pioneer decks are good, check here
for all of them. the mp3 option is totally worth it.