September was wet when I was on the JDF and I'm pretty sure that's normal. It won't be that cold, but don't count on easy fires because the forest is often soaked so you have to work for it if you want a fire.
Regarding guides, there is a JDF guidebook that is decent:
And then I think a lot of people use Blisters and Bliss for the WCT.
I'm not too sure about online resources. I'm sure there's some good trip reports at ClubTread.com