At 14 mph you need to do the 2 day ride or get into better shape. In regards to pacelines let people know you are new and ask if you can join. The groups that won't let you join will be way too fast for you anyway, and if there are any slow enough to be pace lining at 14mph they themselves aren't the best riders either and won't mind new riders.

If you still are thinking about the 1 day:

200+ miles @ 14 mph ~= 14.5 hours ride time. Being generous say you stop on average a maximum of 20 minutes per official stop ~= 7 * 20min = 2.5 hours.

Assuming you can keep your average pace towards the end of 200 miles you'll be looking at a 17 hour total time. Assuming you leave 5:00 AM in the morning that will put you in portland at 10:00 PM at best.

You do not want to be riding in at 10:00 PM by yourself.