[GNC] Am I in business?

[arthur brogard]

Hope this is the right way to introduce a new question/thread.  

I and my ex jointly own four properties two of which are rented out.
We are not registered for gst and are not in business though I have an ABN leftover from when I attempted an online business.
Are we conducting an enterprise?  Will be be eligible to pay GST when we sell any of those properties?
Should we be keeping certain records?
Should the arrangement be formalised as a partnership or something?
What should we be aware of?
I'm putting my personal household expenses etc. into gnucash but not in any really strict or serious way.  Should I be getting that more properly organised?
This is the only forum I know of where I can ask such questions.  If it's misuse of this forum and anyone knows a more fitting place please let me know.
:)
ab