I think the guys in Newcastle did a fantastic job getting Pinfest off the ground and then running it successfully for three years.

If I were considering a similar venture, say in Ballarat  , I would give the organisers of Pinfest several phone calls over a couple of weeks and pick their brains. There will be glaring mistakes that they have made and could be avoided and I'm sure they would be able to offer a myriad of advice.

Piggybacking onto an existing event in the city also makes a lot of sense. It would lessen the risk for you and boost the event for the existing organisers - such as a boat show, car/hotrod/motorcycle show, etc. These events already have a marketing machine in place and already have contacts at media, venues, printers etc and I am certain would only be too happy to have a pinball event tacked on to their existing show. 

Happy to help and support in any way possible.

Attaching it to an existing event is a good idea

The more I think about it, it would be easier to do this in Ballarat or Geelong, rather than Melbourne
Smaller populations would make it easier to advertise to reach an audience