Hi there,
You can use it to manage your existing investments, under the Portfolio Manager memberships. Hence this should be tax deductible, but get professional advice. It also integrates with Xero.
If you have multiple properties, i think the magic number is 3, it is a tool for your business (the ATO see you as being in the business of property) and this makes it a lot clearer.
**Disclaimer: Have been a subscriber for a number of years. May or may not have a vested interest.