a guide would be better. It'd be a really long day if you had to scout everything you couldn't see from the top. Water level advice is spot on too. 1 to 2 feet is what you'd want, doable above or below, but that'd be optimal for a first trip. In the event you flip a boat, you'll re-flip while in the water and climb back in - so maybe give that a shot or two before you shove off.
It's a beautiful run, hope you get it.