I have recently purchased a SX Celica with the 5SFE engine, I live in Australia and would be interested in modded the original engine, I wouldn't mind going turbo but I want to do it as safe as possible, is there much room to move, have many people made a successful 5s Turbo.

Performance wise, I don't know where to begin and I have hard time finding ECU's for the 5s engine

You may swap to 3s-gte(3gen)
All bolt on and ecu 3s-gte

being in Australia I believe you have much more aftermarket support for the 3SGTE/3SGE engines.

A 3SGTE would be "safer" than a 5SFTE