Immigration at borders don't give a stuff, those in immigration offices are pedantic, that's why I bounce. I won't be going anywhere near an immigration office for the next five years
I got my DTV on the same basis, although I have only four in Australia. I simply registered a business name (cheaper than a limited company) and gave myself a work contract which allows me to work remotely. As all my properties are managed by agents, my role is more of an "overseer", I would "work" no more than a total of two hours a week, essentially responding to emails. However it was enough to get the 5-year DTV. I had previously been on a non-O retirement visa, so I was happy to get off that!