Hi Garry,
I just went with the standard suspension in mine with the view of getting the 30mm Seikel lift kit, up in QLD you can't have larger tires and lift suspension together as this van has ESC, so i think the M+S tires i got will be ok and the lift will be better than larger tires, so the gearing isn't changes with a different rolling diameter.
I looked into the gas bottle idea, but quickly ruled it out, as you are right about the compliance here in aus, at this stage we will just use the Butane stove, cheap to run, easy to buy and we do most of our cooking outside and an induction plate for powered sites, if we stay at one.
As for cost, I'm looking at the $95-100k mark myself, I'm a cabinetmaker by trade, so I'm able to do most of it myself, its a great project, but id rather be using it like you are at the moment
Almost finished installing the resomat sound deadening and 10mm reflective closed cell foam insulation, hopefully start on the cabinet template this week, while the RIB bed is still in.
have fun up on the north east QLD coast, we were up there this time last year and had a great time in the warmth