Hi Dunk,
Suggest you start with a map of Sydney - maps.google.com will do nicely, plus that earlier map showing the light pollution.
The basic problem you face is a tradeoff decision between:
- reasonable commuting by train (preferred) or bus (second best),
- light pollution;
- lifestyle (and desirability);
- cost.
I'd suggest you don't make any decisions until you have had time to study the issues first hand for several months. For example, think about the trips you make most frequently (work, shopping, recreation) and actually try making these trips on average days to/from a location you are considering.
Cities here are far larger sprawls than in the UK. For many the sheer size of Sydney leads to the decision that until we can retire to the country, there is no satisfactory solution and instead observing is limited to
- portable gear which can be taken to a dark site on Saturday nights (1-2 hour drive depending on where home is), plus the odd other night if its really exceptional or there is something special to watch, or
- joining a society with facilities in the country that you can use,
- if you can afford it, a weekender in the mountains west of Sydney with the gear set up there.
Note that teaming up with a good friend with similar interests can help significantly if you share the transport.
In the orange zone of the map, that means 2-3 magnitudes of light pollution. Red equates to 3+ magnitudes of light pollution, 4-4.5 magnitudes in the CBD of Sydney (between Central and North Sydney). Yellow on the map equates to 1-2 magnitudes.
To get an idea of the time to commute by train, the timetables are here:
http://www.cityrail.info Add to this the time to get to/from the station at each end. Many stations have a carpark and it is quite common for people to own a cheap old car to leave at the station during the day, though this adds to the cost of living and should be traded against the cost of living close enough to not need a second car for this purpose.
I should add that the traffic in Sydney is very slow on a good day and appalling on a bad one - no quicker than train travel on a good day and quite possibly slower on a bad day - and there are some areas to avoid like the plague if you choose to drive such as Macquarie Park (which is gridlocked for 1-2 hours most days).