Hi, Hidden away in Part 61 and CASA's list of "Prescription of aircraft and ratings" is the details.
(Or on rereading that sentence, perhaps it should be "The details, in part 61 and CASA's list of "Prescription of aircraft and ratings", hidden away, is."
You can do a multi-crew type rating for the Cessnas, and then you can operate as part of a 2 pilot crew (and you'd need an MCC course). The captain would also need to hold an ATPL.
Or you can hold a single pilot (SP) rating for some of those types (500,510,525,550,560) and operate it by yourself, we do. I imagine (following CASA's normal "logic") that if you wanted to do single-pilot and multi-crew, you'd need to hold both type ratings!
The medical required depends on the operation - private (class 2) or commercial (class 1).
CASA does accept foreign type ratings; not sure about the process or restrictions but I know it's not always simple or obvious.