You should find in your POE letter a reference to you having an ETA assigned with your POA but you only need an ETA if flying into Canada.
For insurance I did a quick Google and this company whom I have no info on seem to cover Australians for 2 years on an IEC
https://www.duinsure.com.au/policies/international-experience-canada/
Plenty of people might say take out Canadian insurance which can be an option but coverage can be limited and does not include repatriation to home country should the worst happen. Plenty examples online where people have been caught out by that and been in debt for a long time.
As said plenty of posts here about flagpoling but simply you leave Canada at the land border head for the US side where you tell US CBP you are not entering the US but flagpoling. They give you a piece of paper that says you have been adminstratively refused entry to the US which has no impact on any future US trips.
With this paper in hand you head back to the Canadian side, present your new passport (plus old passport or photocopy old bio page) and your POE plus the US piece of paper and tell CBSA you are there to activate your IEC permit. In your case ensure you tell CBSA you have a new passport versus the one you applied with.
If they ask for insurance it needs to be 2 years else might not get 2 years permit, as for proof funds they may or may not ask for that , and this is a personal view I cannot see a joint account being an issue given you have access to that as well as long as shows access to the 2500 CDN.
The main rule with CBSA is to answer all questions honestly but not to volunteer information or documents that you are not asked for. So dont offer the insurance or POF unless asked.
You may well get asked how long you have already been in the country as a visitor for example so be prepared to answer that.
See here whether you want to follow advice about other documents
http://www.cic.gc.ca/english/work/iec/arrival.asp
Finally check whether there are any border restrictions on flagpoling at weekends for example given some land borders placed weekend restrictions during the summer specifically for example into Ontario from the US due to summer traffic congestion.
Good luck sure you will be fine .