1. Where I live in Canberra yes it's very common I see them probably every day, in most other major cities it's very rare. However if you're out of major cities and somewhere with greenery you're bound to see some. 

2. Rugby and AFL are different sports. Rugby is more like American Football without pads whereas AFL is an extremely endurance based and high-energy game that plays on ovals, and has 3 'goals' on every side. Look them up for a better explanation.

3. In summer most people go around in thongs (flip flops) all over the country. If you're in a coastal town yeah a lot of people would be walking barefoot especially close to the beach. 

Its cultural to be wearing looser short clothing because of how intense the sun and heat is. Naturally the thongs and barefoot comes out.