Scouse said..
If I pick my day perfectly no wind low swell and stay behind the rottnest ferry in the wake and go in convoy with a few people can anybody explain why I still shouldn't.
The ferries these days take action to stop you sitting on their tail. So be careful if you think thats an option.
Your boat is smallish but i see loads over there so that will be okay.
Make sure you've got loads of fuel, enough for the trip plus 20% at least more.
Something to help you sit higher would also be helpful. A Bayliner is designed to be sitting completely whilst being driven so that will put a lot of pressure on your lower back. I often will kneel but its a long way their and back so a heavy cushion that sits your arse higher than your knees.
Other than that watch the winds, check the prediction against the actual winds for a few days before. That way you get a better idea if they are on track.
Last point is don't over stay and think you'll be okay getting back. At least not the first few times. It very easy to be be sitting on the Island and not realise the wind has come up.
Always play it safe and worse case if you must send family and wifey home on the ferry. If you scare them good luck getting them out again.
Study the island maps clearly before hand and fully understand your entry point to each bay you extend on visiting. They look very open when you bobbing up and down, but the big hard reefs underwater can be hard to spot from on the water.
Id more try following a bigger boat like a 35plus flybridge.
Also be careful around the harbour entrance and the Rotto entrance's. They will often have a much steeper wave affected by traffic and that is the spot you will duck the nose in if not careful.
Cant think of many other basics though..Hope that helps.