Mate, no offence, but pretty much all of these questions have been answered before in the forums. Do some searching and I am sure you will find all the info you need. Perhaps not Gen3 specific but everything else you can think of has been answered by myself, Mihai, solongaudi and others.
First thing you need to do when it comes to planning an aftermarket stereo is get Sony xPlod out of your mind as well as Pioneer (except for a few headunits), JVC (except for a couple of amps), Kenwood (except nothing), Fusion, Kicker, Soundstream etc etc etc but mainly Sony. They don't make anything "decent".
Look at websites like
www.fhrxstudios.com and
www.formaudio.com. FHRX is one of the top installers in the country and Form Audio is fantastic as well. They both stock the brands you want to look at, they don't push b/s systems like the sales people at any chain store you can think of. Also
www.mobileelectronics.com.au it's probably the best aussie car audio forum.