Just be prepared for the climb and descent between KM markers 44 and 50. The view is worth it, but it's a doozy.
I'll second that. I did that stretch going south this summer
. The hills are really fierce. Someone told me I couldn't have picked a worse route, they suggested going on I5 was better which may be easier riding but it is a freeway. The STP route will probably be fine except for the Longview Bridge: steep, no shoulder, very busy, lots of trucks. For the STP ride itself they organize motor cycle escorts over the bridge (a sight to see).Art Birkmeyer
may be able to give you better guidance than me. Art lives in the Longview area
If you are taking the ACA route avoid Bremerton the place is nothing special and the traffic is terrible. Send me a PM when you are going to be in the area, if I'm around I'll show you an alternate that's more scenic.