I didn't see an adjustable fuel pressure regulator on your list. You are going to need that before you expand any further, especially if you ever change injectors.
You'll need to upgrade the fuel pump before you get deep into other mods. TR owners will often do this very early in the game to insure they have fuel in the future, but TTA owners often hold off because it's more difficult (but not impossible) to change the TTA fuel pump.
A number of TTA owners will say say that you can run the car deep into the 12's without any other mods to the engine. If you want to race, slicks or drag radials would be the next investment to get the ET's down. Again, for racing a cut-out pipe or gutted cat converter is going to help. If you don't have emissions testing, a gutted cat will really free up the exhaust flow.
At some point the turbo will be a limiting factor a good upgrade. Turbo technology has progressed since '89 and you can find some good choices while retaining the stock torque converter.
Intercooler upgrades for TTA's are not quite as easy or available as a TR. There's not a lot of room to run a stretched IC and the front-mounts have usually been from CAS and often unavailable.
Didn't see how many miles were on your motor, but simple things like valve springs will yield improvement - they tend to get tired quickly.
The one mod that will generate a big discussion is the downpipe
Either way, plan your upgrades so you have the pre-requisites set and can do them incrementally or in small groups.