Hi Mate, I have fished their before in the evening with Pillies and caught a shovel nose sharks and an eel, I am sure their would be other fish around but think best bet would be use a running weighted float with a beach rod as alot of snags in close (first 20-30 odd metres) before you hit the drop off....(I fished just beside the Dog park) which is the green field you can see down the south end of Coggee.
I am sure some locals could point you in a bit clearer direction.
As for Harbour fishing "no clue" but think the City side of the harbour fishing is prohibitted from most of the shore locations....
Do a google search for landbased fishing spots in Sydney and you will pick up all the information you need.
Best of luck and happy fishing....Hope this helps a bit...
Cheers Kev