Have done it several times in single-engined aircraft, mostly via Flinders Island (the distances between bits of terra firma are less) but also twice via King Island and Cape Otway (once at about 1000 to 1500').
Check the weather carefully. It does tend to be worse over the islands than through the middle. In fact the eastern end of Bass Straight is probably one of the most notorious weather factorys in Australia. Think of the 1998 Sydney to Hobart race.
If your aircraft is fitted with HF learn how to use it. Very useful if you have to go low. Set up the overwater schedules. ATC are very good. I was a couple of minutes late on one and they were calling me.
Be very careful if there is a NE to SE wind blowing around Flinders Island. It will bring in sea fog. If you have the fuel go up as it will not penetrate far inland. SW around King Island are a no-go. Very strong winds, low cloud, rain and other assorted nastiness.
With all that in mind. Enjoy the trip. Both King and Flinders Islands are incredibly beautiful and if you care to stay over, both can offer magnificent fresh food, especially seafood. Enjoy.