Okay, read this first.
Turkey info from the resident ifish experts
Can't help you with the Klickitat area, maybe someone else can. As I haven't been out there, I don't know if you duck camo would work. Seems like it might be a little heavy, but if that's all you've got, then go for it. Turkeys key in on movment, not color. I've called in bird to just a few feet away when I was wearing blue jeans and a white shirt. Don't move and they aren't likely to spook.
Full choke will work just fine, turkey choke would be prefered, but I've killed all my birds with a full choke. You can buy special turkey loads, but I think some lead 4's will do the trick. I've killed them with 6's and BB's. If you get them close enough, it really won't matter what size shot you're using. They're going home.
For a beginner (no offense) I'd start out with a slate or box call. Work your way up to a diaphram after you find out what works and how you're supposed to sound like. If you think you're already proficient enough with a mouth call, then give it a try.
Decoy's help direct the turkeys attention elsewhere and are good for bringing in the birds that might otherwise hang up. That being said, I don't hunt with them, but it's a personal preference.
TNN turkey hunting? You're not in Kansas any more. Hoo boy.