Hi Aussie,
I have received RFE's for the DS-230 and AOS, but I don't know if that will be much help with your question
Sydney is a 'Standard Processing Post' - which is why you had to send so little with your DS-230. Many other posts, like Montreal for instance, are Appointment Posts (as you know).
The difference being for the Appointment Posts we have to send in all our civil documents with the DS-230, rather than presenting them at the interview. This is a cause for RFE's of course as they are not always entirely specific about what they need.
As for the I-864, I didn't use the EZ form, however what you have submitted sounds about right. I assume you didn't feel it would be beneficial for you to submit a letter from your current employer and paystubs etc.
Anyway, as mentioned, because Sydney is standard processing basically things we are getting RFE's for are more likely to crop up for you at the actual interview (not that they will as you will be prepared with all your documents!).