welcome aboard mate!
firstly... good choice! the only choice really, the best looking rolla's on this site are all blue so u are in good company. im sure dylan, bill, tom, wei wei and others will agree with me here.
secondly.... facelift model (05) or pre-facelift model (03/04)????
if its a pre-facelift... go to ebay immediatly!
eyelids are readily available, as are king springs if you want to only lower it with springs rather than go all out with coilovers. Kings Lows drop the car by about 35mm which is pretty good for the street otherwise u can get superlows which drop it by about 50mm... depends on the height of gutters in your area!! if u are near canberra... lows for sure... wouldnt go lower. to get it all done and installed and aligned should cost u just under $500... good investment.
next thing u need to do is go to US ebay and buy a cold air intake, either Injen or AEM for best bang for buck. CES (aussie brand and forum sponser) and TRD are a little more expensive but the gains differ from car to car so its hard to track. i'm running an AEM CAI and are more than happy with the power and especially the noise!!
as for audio, i'm loving my rockford sub but really its a personal preference thing, find what suits your liking and what you think looks good and mix and match!
but regardless, enjoy your stivo and especially the looks on the commodore drivers faces when u creep past!!!