An outboard on a boat this big will be a very unsatisfactory solution. While you may be able to come and go from a moorring, you will not be able to maneuver the boat near a dock, as the engine cannot be used alone. Plus as mentioned, the engine may be useless in a seaway.
Can you elaborate more on this? It is something I was afraid of, but I've already got a 9.9 outboard to go on it, and I'm thinking I can hook up the remote throttle lever (what's the term for these?) so that it can be controlled from the wheel.