sounds like you will use most of the gear, if your project ends up like mine you will end up changing you mind at different stages.. in my opinion do everything proply the first time and you cant go wrong, dont try and save money by doing things 'just ok', save a bit more and get it done right..
if you try and utilize what you have you will end up saving some cash..
Your best bet would be to speak to an engineer when looking at thins like steering, running gear and any mods to the structural parts of the body, this way you wont have any problems when it comes time to get it registered.
check out the link for a list of approved engineers in Oz, find a decent one you can go back to for advice at different stages and maybe email progress pics every now and then just to make sure its all above board.
http://www.rta.nsw.gov.au/registratio ... atories_november_2010.pdf