Don't think there is any quarantine period for importation from Oz (classified as Group 1 country). Wasn't when we brought our cat here anyway.
You can check it out at the Agricultural,Fisheries and Wildlife Dept website:
http://www.afcd.gov.hk/quarantine/animals_e.htm
Plenty of garden flats in DB where the dog can run around - rents are a bit higher than 25K now though.