I did this exact trip with a friend at the beginning of March.
When we did it the water level was fairly low - about 0.65m at the Collingwood Bridge gauge.
It was a great trip - neither of us had really packrafted much before, we had no problems though. We portaged Log Jam, Nasty Notch, and one of the rapids in Decension Gorge which was too low to run properly, but ran pretty much everything else.
As far as typical conditions go, I don’t think there are any! The day we went down the river was at 550 ML/day, which is low, but the week before it was at over 16,000 ML/day, which would be high flood. A week before that it was at around 800 or so. You would probably have seen this already but Hydro publish the flows and rainfall on http://www.hydro.com.au/system/files/water-storage/Web_Rivers_FranklinRv.pdf.
My advice would be to do the whole river section from Collingwood Bridge to Irenabyss in one day. That took us about nine hours. It avoids the possibility of camping midway on the river overnight and having the water level rise alot during the night. There are lots of good campsites at Collingwood Bridge a short distance upstream from the bridge, so you can get an early start.
I would also take packrafts with cargo flys, if you can get them. The rafts handle much, much better with the weight lower, and are still easy to portage.
I’d also keep the weight down as much as you can - the climb out of the Irenabyss is pretty solid.