Hey! Here's where I can help. The coastal section in Oregon from Astoria to Brookings is something I'm familiar with. The ride will take about a week, there are a number of state parks to camp in (free hot showers, $4 hiker/biker sites), and the scenery is spectacular. Especially if you do it in September. Prevailing winds in the summer run from the north so there are great tailwinds if you're heading south.
If you catch the road after Labor Day (first weekend in September), all the better. Fewer RVs and summer traffic. It's a very popular long-distance touring route so there are bound to be other cyclists heading in your direction.
Off of the top of my head, these are the places I camped:
Nehalem Bay State Park
Cape Lookout State Park
Beverly Beach State Park
Honeyman State Park (very nice)
Sunset Beach State Park (very swampy but the best showers)
Humbug Mountain State Park
No need for reservations. There's always room for a bicyclist.
Good luck!