I've identified 1-2 food products which I think could work in the context of Australia. How do I begin!? How can I repackage the food in a contemporary consumer-friendly packaging? How do I get health shops or supermarkets to adopt it? Should I do Social Media marketing? Where do I begin?? I'm willing to spend about $4000AUD to start on this.

I guess you work on your own and you are planning to purchase the product from a manufacturer and then resell the goods. It looks like you are planning to take all the tasks and responsibilities, and that you have some idea of who are your buyers, probably you will become a distributor yourself. If you are just starting, I think this article could help you find some ideas about what needs to be considered or with what kind of people you will need to deal with (manufacturers, distributors, retailers, salespersons, etc): https://www.entrepreneur.com/growing-a-business/how-to-start-an-importexport-business-entrepreneurcom/41846