weeeeeell... once you start upgrading, you'll want more boost since it's the only real way to get a LOT more power, and with that comes certain limititations. Head gaskets are weak on these cars sicne the torques spec is so low from the factory (very odd on a toyota). Once you hit more boost, you'll also hit fuel cut, so you'll need to get an FCD or do the 550cc injector/lexus AFM swap.
Great car, and if you don't mod and push more boost, the head gasket should last you for a while. If you still have the old sawblade wheels, keep em and put some sticky rubber on em and race it
Also, it seems like you have the money, so you can instead dot eh Wilwood big brake kit instead of the brembo / kevlar pads. Not cheap, but very nice looking, and Wilwood knows what they are doing, so performance is going to be even better than they look.
K&N air filters are good, but there is better. I noticed you didn't talk about upgrading suspension components... I notice it has TEMS on it, some people here love it, I don't have it, and it does limit selection of the types of shocks you can use. I myself will be upgrading (once I get the money of course) to a TEIN system with the in car adjustability which is like TEMS but better.
In the end, I could go on and on, have fun as it is, upgrade and have fun doing the work yourself
