I don't think Crago is suitable - too light polluted to show the Milky Way well, and I suspect they are looking for access to a large scope on an equatorial mount in a permanent and secure building which can accommodate cameras attached. Mudgee or Grove Creek perhaps ?
For cloud cover in the blue mountains:
a) check what you can see on the webcam at Katoomba Scenic World, prior to 5pm.
b) call someone you know in the blue mountains who can stick their head out a window to have a look.
c) the BOM, which issues forecasts for Katoomba and also has hourly satellite photos:
http://www.bom.gov.au/australia/satellite/index.shtml
The live AWS data from the BOM Mt Boyce weather station may also be useful.