I used to have one(now in an altezza). It was great barring a few mechanical mishaps.
If you touch the exhaust, keep the CAT, it stops a lot of the tinny/drony sound.
Swap the stock air filter for a TRD or other high flowing item, no need for a pod setup, it just makes the AFM read funny on part throttle.
It had the TRD sportivo suspension kit, and it was phenomonal, I rode in one with Tein gear all round and it was a bit firmer, but still ok for the wife.
It had a stiffer rear swaybar, which was great, but it needed to have the suspension bushes made firmer as it made some clunking noises when entering driveways caused by the bushes being too soft.
Light weight mags make quite a difference to how it felt to drive, I had wedsport 16" somethings on it, and tried some Advanty(?) 18"s on it, and it was (very) noticably slower to accelerate.
Have a search through using RunX and you should find pretty much every post I made about it.
Changing the lift point below 6000RPM will lose you power... the only guys I have seen(read about) gain anything by lowering it, have been guys slapping turbos on them.
From factory they have 4-2-1 headers, with a very very good finish on them, I doubt that you could get anything better designed barring the TRD items which are a 4-1 design, so would sacrifice lower RPM torque.
The 2zz power FC for the Celica is not a straight fit item, you have to re-wire it a bit. There is a company called brashboy that modify them for the 2zz Corollas for an exhoribident price.
When I was looking there was nothing available to modify lift point, all the camcon type controllers weren't able to do it. Some dude on newcelica made a manual one, that they then managed to put on an RPM switch, but after tinkering on dynos found that the factory switch point was pretty much ideal, barring some that lowered it to 5800, but anything below that lost power.
tuning at the lift transition point is apparantly very tricky... its not my area of things, but thats what I have read.
C-one do some funky stuff for them.
have a looky here too for some info on them.
http://dave.net.nz/old_site/id48.htm