We camp a lot at Fort Stevens. It's one of our go to places.
I guess you are looking at the KOA across the street from Ft. Stevens...not our style but for kids I guess it's a good choice. (video arcade, bouncy house, etc.).
Bike trails at Ft. Stevens are absolutely first rate. Miles and miles and miles of them, all well maintained and paved. You can easily get lost and wonder around circling and looking for a way out, but they are somewhat marked with signage.
There is lots to do in Astoria and you can wander down to Seaside for a real tourist adventure....shells and t-shirts, cotton candy and merry-go-round.
5 Miles from Ft. Stevens has exploded. Costco, Home Depot, Super Walmart (in construction) and every kind of strip mall stuff.
Have a good trip.