Everyone has their preferance, most people go by price though which is logical I suppose. Intake
is probably a first for most, be it CAI
or SA, and usually if you want a Performance Air Filter
you'll get it at the same time as your Intake
makes the best CAI
is pretty close I think) and Blitz LM and SUS are the best short-rams.
Then most people usually go with exhaust, TRD
gives the best legal gains over any other product out there. Dual exhaust will decrease Performance on a Celica.. don't go there.
Headers, typically most get them after exhaust and other parts but apperantly you can get just as good gains and satisfaction from a header without other mods.. Trial is suppose to be a great header on it's own. AEM
pulley is fairly cheap and is pretty beneficial, suspensioin work is always a plus too, it lowers the center of gravity on the car (good for cornering, acceleration & braking,) and I believe it reduces some wind resistance. Grounding kits/wires are pretty cheap and have decent benefits, no big gains but they enhance torque a very minimal amount, gives better flow of electricity throughout vehicle, can make the car idle better..other benefits too.