i put 25mm spacers on my rear wheels, LED angel eye conversion, LED interior lights, licence plate LED lights, using a K&N panel filter in place of stock one-> have plans for a AFE CAI, ganna weld in an xpipe in place of my resenator,
some people talk about software upgrade for the engine and tranny from BMW, but i dont know about this personaly
i would get my IS tuned after intake/xhaust, should get more power/smoother powerband/mpg
i dont know about buying an overpriced cat-back, the stock muffs are pretty small and prolly flow pretty good already, just cut ur resenator
if u have too much money u can buy supersprint headers for an insane price,
i havnt been able to find any supercharger/turbo kits myself, but u can customize anything with a turbo/charger from a real good shop
or get a proper shop that has skill to build u a sick 3' xhaust
ECStuning has the LEDs, spacers, CAI
DINAN has the software, CAI, throttle body
supersprint has xhaust, but i would just cut the stock resenator
headers are an option but i have only come across supersprint and then u need a tune to cancel the O2 sensor
do not dump 2+gs into somthing (cat-back) that u can get custom from a proper exhaust shop with all mandrel bends 3' stainless steel xhaust for cheaper