dual occupancy conversion?

Hi

I’m finding this subject hard to research.
I’ve seen quite a few double storey houses that have been converted to a dual occupancy (on the net), and am thinking of doing this myself.

But I have a few questions –
Has anyone done this, and what problems did you come across?
Does the first floor have to be fire-rated?
Do the tenants of the ground and first floor share the backyard, or do you have a fence dividing the backyard?
Is it noisy for the tenants living on the groundfloor?

We may even purpose build an investment property such as this. For various reasons, I don’t want to do a duplex (strata or torrens) that we can sell separately.
We’re in NSW.

thanks,
Spirit