I did a few courses with Yachtmaster,
yachtmaster.com.au/sailing-school-courses/but in particular I'd recommend the coastal navigation course, and maybe an introduction-to-sailing course.
In a TopHat you might have an outboard rather than a diesel, so familiarity with those engines or a book will help resolve mechanical issues. When you're about to set off, a licence for a VHF radio will be a good idea too, it's only a 2 or 3 hour lesson, and a simple test the next week.
So, 2 or 3 short courses, and then you should practice sailing. Like Cisco said, it's cheapest to sail someone else's boat, but there is no substitute for sailing as much as you can. You will thus experience weather, tides, currents and navigation issues, and you will learn from doing it. A night sail is the next extension to your experience. A few hours at night in good weather, to a safe harbour or previously-visited place will give you good experience. And a bit of coastal sailing will help later. Day sails first though. Build up your experience, with practice, reading and some appropriate short courses.
I'm in Westernport and will resume some sailing this summer, so some coastal passages are available if you like. 28 foot Compass, outboard motor.