Most head units come with a "cradle" that the unit slides in and out of. From experience this won't fit into the Double-DIN space of the VZ, the unit should fit reasonably snug.
Your options I believe would be to remove the factory cradle and use possibly and Aerpro kit from Autobarn or similar OR
Secure it to the factory cradle which I believe would be far more difficult unless you can figure out how to access the sides of it for the screws.
As for wiring, being a newer model it should be pretty simple to use the wiring plug from the new unit and splice into the existing one.
I would strongly suggest splicing in BEHIND the plug rather than chopping it out incase you ever want to revert back to the factory unit.
I would even strongererer suggest just buying the harnesses from Autobarn/Supercheap etc. It will take no more than 30 seconds to plug both in and have your unit powered up and good to go compared to the headache and risk that splicing can be. You will need a Holden-Univeral Plug then Universal-Kenwood (or whatever brand) Plug. SO easy a monkey could do it! Ill see if I can find you some links
