I love it when people threaten to take you to Fair trading. What do they think will happen then? The StrataKops will guard their unit while they tear it apart.
Your owner needs planning approval from council and a set of special resolution by-laws from you before he does anything else. If he is not prepared to provide these, then don’t even bother with Fair Trading. Apply to NCAT for an interim order to stop the work.
If this owner is as ignorant of basic strata laws and procedures as he seems, then I wouldn’t hold out much hope when the work is done, the bathroom leaks and the walls sag. Even worse if he “flips” the unit, the responsibility for alterations to common property will fall back on the owners corp.
Talk to an experienced strata lawyer ASAP.