Is this campsite first come first serve? I can't seem to find any information on this?

WA discovery pass required. First come first served AFAIK.

Yes, with discovery pass

Yea, first come first serve

The annual northwest forest pass is what they ask for?

Yes it is first come first serve. It’s DNR managed, not USFS or state park which is why you probably won’t find much info on it online anywhere