Having just paddled it a couple weeks ago, I'd say you could easily forego the lower north fork. It also is a very bad idea for beginners, because there are 4 fences you must portage and climb over/under. If you were to swim they are almost all a definite strainer. When I went tons of wood was collecting in them and would easily collect a person and cut em up.
There is maybe 1 or 2 at most stretches that had waves for more than 25 yards or so at once and the rest was a bend in the river that you paddled through a swamped marsh with fast current to negotiate a boulder at the bottom of the turn. Also not a great place to swim. Nothing hard, but not really good places to be out of your boat.
The paddle across the res is not terrible, but after all the portages isn't fun. My 2 cents.