Hi Bowerboy,
I have never participated in this event however, I have spent a lot of time on the Murray on canoes for up to three weeks in length at a time.
What I found to be the most challenging factor is the wind. November is typically windy and the twistey nature of the river means that you will be affected by the wind from all directions during the day. You can bet your bottom dollar that it will never be behind you either

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As for the current, I found that it was usually around 4-5km/h which sounds alright but be prepared to be blown upstream if wind is any more than about 10km/h.
I definitely don't want to discourage you. This sounds like an amazing event and I would love to participate one year as I think it would be a lot of fun. However, be prepared and spend some time on the river before the event and get some km under your belt. I would absolutely want a 14' board for this event. Something you'll feel comfortable on for days on end will be paramount.
The above post post might be helpful if you can get in contact with the bloke who has done it already.
Best of luck mate