Sharrn,
I did that ride many years ago.
I road from Tigard Oregon (suburb of Portland) via Astoria and down the coast to Florance then back to Eugene. I found the first leg to Astoia was around 70 to 85 miles and it was a work out. You will be crossing the coast range so figure great down hills and slow up hills. If I had to do it again I would camp in between Astoria and Portland. Try to figure about 40 to 50 miles per day to make the ride enjoyable or else you will find it to be streesfull (both mind and body) doing more. I have done my share of 80 to 100 mile days and tends to be less than desirable Its a fun run to Tilamook take your time to enjoy it. Don't forget to visit the cheese factory.
Liam