you wont be able to go full show and full go on a celica. unless you dont care how fast it goes in comparison to the $$ you spend.
also my advice is dont buy it new. buy a 2000-2002 model and work from there. since you want to redo so much of it, new or used is of no difference.
N/A you can hit 12's with weight reduction, good driving, and the correct mods. It will cost a lot of $$ though.
on an 03 - 04 you'll be stuck in the 13's no matter what.
F/I Turbo with an 03 you will be stuck at mid - low 13's. maybe with nitrous + Turbo you could hit 12's when you learn to drive it.
with a non DBW you could see 12's with Turbo and low twelves with Turbo + nitrous. or you could go S/C and run mid 13's.
Dont count on the 3sgte swap cause it's still never been proven to work and be driveable