KityKat

I currently have a nice 4-8kg rod from a tackle shop paired with a 2-4kg Shimano sienna 2500 and wanted to replace it with a shimano sienna 4000, but now I have the dilemma of what pound line I should get, I am located in Wollongong, and was thinking of at some point mabye trying to catch mackerel, but usually just Bream and flathead.