SteelheadMan,
Seein's all the "heavy hitters"
here are being close lipped I'll try to answer your questions.
F4 is pretty much open to any part of the river that you want to fish....but the after fishing party will be on Sand Island which is across from the mouth of the Lewis River on the Oreo side.
Tying a moochin' rig is simple, just tie 2 bumper tie's about 4 inches or so apart, the distance depends on the size herring that you will be using. As for the herring question the color depicts the size of the herring, I think it goes yellow, red, green, blue, purple (smallest to largest, red was the hot size last year).
When I troll the Columbia I use 4 to 6 ounce weights on a three way swivel with a drop line of about 2 feet, depending on how many people are in the area and how close to the boat you need to keep the gear. For anchoring up and pulling K'fish same 3 way with a drop line of 3 to 5 feet (experiment here) to the sinker (2 to 4 ounces of lead) and 5 feet to the plug, that will put you in the zone.
Any ol' tackle shop should have magic thread. I have had to special oreder sardines here in Olympia, but have heard that stores around the Columbia carry them in stock.
As for a rod I really don't feel you need to spend a bunch of money, I use my $35 Shimano TDR downrigger rod for springers as well as in the salt and it works just fine (No comments from you Gizmo!!! :p ) and 20 or 25 lb test is ok fine.
Think I covered it all.
Good luck and tight lines, Jeff