Having experienced your sky just down the road in Wandsworth whilst on a fishing trip, I can pretty much guarantee that even a modest sized perform well!
An 8" SCT on a tracking mount is great for the moon, planets and globular clusters (and sun too with an appropriate front filter)
A bigger Dob will be amazing on everything, especially the fluffy stuff - I found that the Skywatcher 14" is a great compromise. Great views, big enough to be impressive but not so large that it is unmanageable weight wise.
I would say that with that quality of site, you could easily tempt some of the larger 20"+ dob owners to venture down from Brisbane for the weekend to lend a hand (especially if it's in Trout season
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