In august you will have your hands full with coho and even some fall chinook on all 3 rivers you mentioned.
spinners, corkies, yarn, bait, and plugs are the most often used things in the fall.
Anywhere from 10 up to 20lb mainline is average.
I drift fish with a fly rod and it's a lot of fun, but I don't traditionally fly fish so I can't help you on regular flies.
Do a search on this forum with the keyword "coho" and you will have more info that you need.