I would use Rails. Rails has everything I need to build a web app and API back end should I require a native mobile app. As a ruby guy I can't really comment on the frontend, but my go to JS framework that lets me build shit quickly is knockoutjs.
If you're interested in narrowing the location to just sydney - there's a growing FB group called "Sydney Startups" (https://www.facebook.com/groups/sydneystartups/) and a related monthly newsletter which features Sydney Startups -> sydneystartups.com