Congrats on your purchase. You dont see many TI's on the road these days.
-In terms of power,you're not gona gain much with small mods like an exhaust system and ECU updates..... you gna have to turbocharge the motor to see serious gains and thats gona cost you.
My suggestion to you would be to done all the preventative maintenance on the car and enjoy the car for what is it. After all these cars do/should give most normally aspirated cars(2.0l and below) a run for their money.
Stuff you should look at changing at this mileage:
-water pump,thermostat and cooling system pipes
-all 4 coils and plugs(NGK or Bosch)... must be platinum plugs
-clutch and flywheel......A slipping clutch can affect fuel consumption
-All filters
-your fuel pump could give you issues around this mileage, would be wise to change it aswell
a 5w40 oil is what I use, it works for me.