firstly you cant get an STI B4... from 1999 anyway (to cover my arse) in case you can (09 has an sti i think)..
your B4 should just be an RSK.. RFRB... RFRB is just a visual styling im pretty sure..
two ways to lower your car..
#1 low or super low springs - not requiring a cert, more for looks than performance
#2 get adjustables, requires a cert and for performance
mags
you will be looking for a set of 18*7.5 or 18*8 rims.. that will take 215/40/18 rubber (or similar dimensions)
Depending on the offset its likely you will have to roll the rears (this is dependant on whether you have lowered your car(obviously))... you need 5*100 stud pattern as well... fyi
offset is not totally accurate measurement, just go and try some rims, some go +40, some more some less... some +40 will fit, some wont etc.. i think you get the point
Twin turbos
primary should be be 2200ish to 4400ish and 4500 to redline for the secondary. Decreasing the VOD you can get a professional to alter the wastegate on the primary or go for a sequentail controller (not boost controller) and that all most eliminates it all together.. thinking aboug $400+, brand name eludes me. the manual way is more of an art and doesnt give as good a result as the controller. (i had manual way on my old gtb and worked just fine).
Hope this helps