Criminal Behaviour

It was my understanding Australia has much more draconian laws covering this type of behavior, much more similar to US CFAA rules that broadly criminalize everything that isn't explicitly permitted. At least in comparison to the much more sane EU rules that is. Given that being true it wouldn't be out of the realm for a prosecution to happen in Australia if someone wanted to spend the time and money to get Australian law enforcement involved but it would likely take significant time and very significant amounts of money. (it would probably require hiring a local Australian lawyer to do the leg work that would be required). There's also the option of getting an Australian court to issue the equivalent of a do not contact order because of the past behavior. Subsequent bad behavior after that order would be much easier to extract penalties from.

In addition, the actions of impersonating people, and several of the other actions listed could probably fall under Australia's defamation laws which IIRC aren't that different than the UK's if someone wanted to go after him Civilly.

As always in these situations the burden is on the harassed because the internet makes harassment a million times easier.