I would suggest the very first legal 'issue' to consider is the actual structure of your new business. Changing structures down the track can be tricky and costly so best to get it right at the start! Usually an accountant or solicitor can help determine the best structure for you and ensure personal assets etc are protected.

Once you've determined the right structure - ensuring you are registered properly, have the right permits/licenses and insurances in place is crucial. The Australian government has a business license information service (BLIS) available, where you can search in your state by your business type to determine any permits or registrations you will need and requirements you need to meet. 

Other legal issues to be considered during start up phase could include:

• Rental/lease agreements; 
• Contracts with suppliers (for example, graphic designers, website designers, manufacuturers, wholesalers etc)
  
• Terms and Conditions for your website and/or for purchase of your products/services
• Agreements - generally and varied depending on nature of business, for example - employment agreements; terms of service agreements; contractor agreements; confidentiality agreements; distribution agreements etc etc
  
• Intellectual Property requirements (make sure you're not infringing rights and make sure you are protecting your rights)

Others may also apply depending on the nature of your business but I would suggest that the above applies to most new businesses in some manner.