Welcome D.
Glad you find the site informative .... I've learnt heaps from the knowledgable people who contribute and share their info. It's a two way street so hopefully as you become more experienced you can also help other newcomers.
In regard to Heathcote ... I remain goldless BUT others do quite well there.
Take a drive along any of the tracks and you will find evidence of diggings, one is as good as the others, just have to walk over it.
The One Eye area has accessible areas with lots of old diggings but also a lot of shotgun pellets, if you're detecting those then you'll also detect gold if it's there (dig all targets!!)
At least it's reasonably close to Melb.
Not sure about the Eureka Gold's capabilities, most gold I've found has been with the SDC.
Your partner may struggle with the 705, I started with one (still have it) and it was a heat tool for learning about detectors but most of my finds with it have been at the beach, have also used it in the goldfields but only found lead.
Good luck out there and don't forget to share your findings, good or bad, if you use the sites search function you'll leo find some further info on Heathcote.
Cheers T.