Obelix said..
If you can uphaul comfortably on your board, go for it.
If the floatation is marginal, you better learn how to water start first.
And this means being able to uphaul comfortably on water which will be much choppier than the river.
Try a souwester at Pinnaroo or Leighton. You won't encounter much of a shore break but you'll get used to sailing in the chop.