if you want a nice rumble w/o bein obnoxious i would look into the magnaflow cat-back...pat(silvert/a) has it on his and its exactly that; sounds good w/o bein LOUD...also it can be had MUCH cheaper than a 100k mile used corsa on a good day, and its stainless so theres no rotting worries
as for headers/y-pipe i have no idea tho i would look into whatever headers/y-pipe foff had on his 98, that was a damn good setup
DEFINATELY get yourself an aftermarket airlid; the stock air baffles should be burned or something similar...these are a very inexpensive way to make good horsepower...also look into the fast toys ram air kit for ls1 cars...compounds with an airlid to make even more hp
if you have a 6-speed car then 4.10s are doable but you seem to be someone who would be ok with 3.73s...if your stock gears are 3.23 or 3.42 then you'll be fine for the time being regardless of what tim says
in the way of suspension a good torque arm, lower connecting arms, and panhard bar will do a great job gettin power to the ground...i would look into gettin a set of drag radials mounted on some crap wheels for when u wanna have some fun
also make sure to check out
http://installuniversity.com under LSx...tons of do-it-yourself LS1 mods and basic maintenance procedures, read through a couple of articles and you'll know plenty about what you have and what you can do with it
and last but definately not least GET A DECENT TUNE especially if you modify the car at all it will definately benefit from a custom tune...and bill(foff) is very inexpensive and usually a cool guy to deal with(and its fun to make fun of his pokemon tailights!
)
good luck dude and enjoy the car...oh and GET UP SOME PICS!!!!