Welcome!
My first u13 sss that i had (which was written off about a year ago - see the pic in my sig) had 17" lenso mags, lowered king springs, full 2.25" mandrel bent exhaust with hi-tech extractors, tinted windows and viper pager alarm. I originally had a cannon on the exhaust when i first got it done and IMO it sounded absolutely crap, so i got rid of it and put a sports muffler on. I would highly recommend not going the mandrel bent in 2.25" as it made my bluey too laggy off the line and was extremely droney and irritating.
I also sourced clear indicators for the front bar (from the USA) and side (from 999 automotive in brissie) for it.
After she was written off, i bought another, which has remained stock standard as it is just my daily driver, while my skyline sits in the garage.
Simple, inexpensive mods you could start off with would be: pod filter and CAI (cold air induction), clear indicators also give the car a nice fresh look, and you could also start with a cat-back exhaust. Ka-bluey had cat-back on his, with an R33 muffler and it sounded pretty good (not too sure if he's still around on this site these days though). As for alarms, there are a few guys around here that are installers or at least know where is good to go (depending on where you live)...