224 is great. Amissegger from Boring to Barton is a little narrow, and slightly busy, but you should be fine. 224 from Barton to Estacada is completely flat and has a generous shoulder the whole way. Past Estacada, the traffic falls way off.
One VERY IMPORTANT THING: about a mile outside of Estacada, you'll see the PGE Westside Hydro Project. Ignore the "Dead End" signs and take that turn, and go around the gate at the end of the parking lot. You'll get to ride a beautiful, flat road that winds through the woods along the river with no cars rather than slogging up a 2 mile, 8% grade with cars zooming by. When you rejoin 224 in 6 miles, you'll be nearly to Promontory Park, after which the traffic disappears almost completely.
Finally, there's plenty of potable water at campgrounds until you get to Ripplebrook, after which there is none at all until maybe Breitenbush.