I'd highly recommended picking up a copy of "Fishing in Oregon: The Complete Oregon Fishing." It provides maps of the various rivers and discuss their put-ins, take outs and popular drifts.
Otherwise, speaking from limited experience, the lower Wilson has been a rather safe 6-8 hour run. You'd put in at Mills Bridge and take out at Sollie Smith. The put-in is just the side of the river in relatively slow water, so you'll need to be careful. The take-out is a steep concrete ramp just above a bridge, so be sure to know where it is and get over there to line it up well in advance.
I think 4.5’ or so is the cut-off to run that stretch without having to walk the boat through parts. Likewise, I wouldn’t recommend it when the water is up over 2000 cfs, as missing the takeout could become a problem. The river forks in a few spots at lower levels and you have to look it over before deciding—while always keeping an eye out for fallen trees and/or overhanging branches. Some of the currents will take you right into them if you approach them wrong.