Sorry, can't offer much advice on the transportation but good luck with it all, I know from transporting all my household belongings over to Australia how much work it can be. I looked into shipping my car but gave up as that had even more obstacles but didn't have a boat back then.
If you wanted to check out the local prices of used boats to help decide if it is cost effective to transport your boat, one of the popular sites is: boatsales.com.au
not many RIBs on there but there are a few.
Dunbier trailers are popular around here as they are made in Braeside, not too far from Mornington. Apparently at peak sales times there can be a bit of a wait to get one.
Just as a bit of additional info, VicRoads do the boat registration and you need a boat operators licence from them: Motor boat licences - VicRoads
Also some of the regulations at Transport Safety Victoria where you will find information on all the required gear: Recreational maritime - Transport Safety Victoria
And finally, to whet your appetite, a bit of info on the local area from Parks Victoria:
Parks Victoria - Bays, rivers and ports
, a couple of useful books: Creeks & Harbours of Port Phillip & Westernport