4. The house and land packages state that site cost is fixed apart from rock removal and concil / developer requirements, roughly how much will these extras are?
This depends on the soil type. Once the soil tests are done you will know what level of slab you will need.
Evap in Melbourne is stupid, it just is not dry enough here, we generally have a lot of moisture in the air and as such it just doesn't work too well. On top of that, any 35c day see's the best of systems struggle. Spend your money on go a refrig system. I can personally recommend the Actron systems, it is so nice having variable temp's in EVERY room. Best of all, our house actually stays cool and we do not have to have doors/windows left open when we go out for a few hours.
We upgraded to 6 star heating and we have since dumped the crappy continuous/solar hot water system installed as standard, our last gas bill was $23 down from $197. Will be interesting to see another winter with this new instant/continuous hot water as it no longer has to keep the solar tank boosted.
We got the main things done such as any bulk heads we wanted, extra wiring etc we did ourselves over a weekend when house had been roughed in, mark it all in a map and all is good. You will find it is cheaper to do most things yourself afterwards. My wife wanted extra noggins put in the bedroom and laundry (wall mounted TV and dryer). We were charged $120 for 2 piece of 600mm width 2 x 4's. Cost me $6 to come down and put up all the ones I wanted in the other areas.
Stamp duty, curtains, tv aerial, there are so many small things that you need. Curtains are the most important, get these done once the house has been plastered and confirmed once all the archs are in.
Good luck with it all.
Edit:
I should add you should always seek permission from your supervisor before doing ANY works on site through the build.