If you look there are some very good Duke owners web groups. There aren't many in Australia, so real experience is thin on the ground.
Not sure where clearedtoenter got his costs, but I would expect insurance to be $6-8k depending on value and depending on airport hangarage will be $5k to $12k pa. I would be expecting an average annual to be $15k, with the potential for the occasional one to be double that or more.
There is also a conversion that puts Walter (now GE) turbines in it, which may be a better thing.
You could end up putting a lot of money into an aeroplane with questionable parts support and questionable resale.