Port Phillip Bay would be good for you to start with, you're about 35min from Mt Eliza.
Western Port I'm pretty sure is just all mud on the north end and I've only really done flinders but that's about 50min from you.
Dive buddy I'd definitely say is a must. Safety first.
Mask and Snorkel would be handy to have
Can't think of any spear guns to look away from...
Any sling / spear gun should have some level of capability of getting a fish...
* There are a lot of topics on these forums, lots of info to be read. A lot of your questions would be answered somewhere or another