I'm basically in the same boat as you trying to learn my way around the waters. I can't speak about the Cowlitz but yes, the Sultan to Ben Howard drift is a good one and I've also been out on the Snoqualmie a bunch from Plumb Creek down to Fall City and also Fall City down to Neal Road or even all the way down to Carnation (very long float). Plumb Creek has one tricky part but that's it. I like getting out on the Snoqualmie right now even though it's not producing because I've only seen one other boat. Good learning water. Good luck.

Bruce