A: Many businesses just need an ABN to get started. Some businesses need a licence, others don't. Best to check with your state business regulator, if you're not sure. To find out if you need to go down that track, best to have a chat with someone already running a business like this nearby.
Like in NSW, the regulatory authority is Office of Fair Trading: here are some notes on licences:
http://www.fairtrading.nsw.gov.au/ftw/Tradespeople/Home_building_licensi...
In Victoria, the licensing authority is Consumer Affairs
http://www.consumer.vic.gov.au/businesses/licensed-businesses
South Australia, Consumer & Business Services
http://www.cbs.sa.gov.au/wcm/licensing-and-registration/
Western Australia, Small Business Development Corporation
https://www.smallbusiness.wa.gov.au/business-life-cycle/pre-start/busine...
Queensland, Tasmania ABLIS
https://ablis.business.gov.au/pages/home.aspx
Northern Territory, Dept of Business, Business Licensing
http://www.dob.nt.gov.au/gambling-licensing/business/business-licensing/...