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I think a key question is how deep can you go before you hit rock. In the Blue Mtns there is a lot of rock around. Do you know what is under the surface where you want to put the obs. Some might argue for a good solid cubic metre of concrete for a pier footing, but if your pouring it on rock smaller might be better or drill the rock to stick some reo bar in there.
Are you thinking steel pier on a concrete footing or a concrete pier in a form with reo? If a concrete pier, a continuous pour from the footing is best. My pier is a continuous pour, wet on wet. You just leave enough setup time for the last footing pour to support the pier form and pour. I used a big PVC pipe as my pour form and left it in place because it provides a nice finish. Insert your J bars for your top plate as you finish the pier pour. You can buy the J bars at Bunnings, they call them foundation anchors I think, near where the reo stuff is.
I don't know about slab stuff, my obs is on timber posts with the pier coming up through the floor. Houghy did a massive pour, ask him.
Hire a digger. I dug my pier footing by hand, and my post holes, damn near killed me.
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