I would pop test your injectors, adjust throttle linkage, and do your IP timing before undertaking any of these steps (save valve adjustment, which is needed anyhow).

As others have said, modifying the exhaust system won't do much except give you a louder exhaust.
A larger turbo is not necessary unless you change/modify the IP. A manual boost controller is much cheaper, easier and more predictable. You will get noticable results by upping the boost to the existing turbo. But making sure everything already on the car is working well (injection system, air and turbo intake, throttle linkage) is needed first.

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