The WA licensing website states that if the boat is 16' or less, and the motor is under 10 HP (hence the 9.9's) registration is not required. I have a copy of the reg in a zip lock baggie in the boat, because I know sooner or later a law enforcement person is going to challenge me on the issue.
As far as the options, I would concur with 3rd oar and oarlock, PFDs, side pull rear anchor, dry storage under the front seat and a fish box under the rower's seat. Rod holders are a must if you are going to pull plugs. I epoxied a small line level on the face of the front deck of my boat; the passengers know if the boat is level at all times, and it makes rowing the boat in a straight line much easier.