If you book business class on Emirates , you will get business class lounge access
I wouldn't be paying $100 extra just for the FF miles - you would be better off just buying some miles in a sale if miles are important
Given the journey time, I wouldn't be doing SYD-BNE-CHC unless was planning to visit BNE. Flying 1.5 hurs to BNE to end up 210 miles further from the destination than from the start point and then spending a couple of hours in BNE when you could , by this point, be in CHC
Dave