I was looking at the same route earlier today. There are a number of ferries, cost varies depending on route but most seem to only travel at night. Dogs not allowed inside or in cabins. Looks like a nice round trip.
Ive been considering the same for July/August but I think Ive decided just to drive straight down the Croatian coast to Montenegro. Maybe save that trip for retirement. Have been to Croatia a number of times but never to the bottom.
Its a great country and I do think that the sites are cheaper compared to like for like in other countries.