I am with StuM. Getting your tri through AMSA requirements will be very hard and expensive or impossible.
Carrying 10-20 kayaks is nothing special. At least one whale watch boat
I know in the off season does that type of day trip.
Surely any place in Australia that has the potential to sell 50 tickets+ a day to day trippers already has boats servicing the market?
The only place I can think of is Tin Can Bay/rainbow beach. But there is not much of interest in these areas for day trippers. Unless mangroves murky water
, mosquitos and sandbanks are your thing?