In my opinion, the 30-40 pound river anchor mentioned is the popular choice. Fisherman's Marine or several other local Portland or Longview shops have complete systems for sale. As of scope, the usual 4-6 : 1 should work fine, just make sure to back down on the anchor a little to make sure it is holding and adjust scope as necessary. It is critical to keep control or all loose line and to have a knife handy just in case. I keep my line in either a plastic bucket or a milk carton type plastic box.
The lower river is straightforward but it gets tricky up by Bonneville. Your plan to start low in the river and work your way up should be just right.
The two fatal anchoring fatalities I consulted on involved sinking by the stern and a passenger entangled in loose line and pulled over the side. I think that BPA publishes a free anchoring guide that is very good.