What size motor would be best (or do you have) for ...
I think it depends on how much you use your current motor. I''ve got a Honda 2hp for my 27'' boat (2450#) and it gets the job done nicely at 5K and 1qt fuel/hr at full throttle. But I sail in & out of my slip. I only hang the motor few time a year to get back to the slip. The rest of the time, it''s secured below. And while it only weights 28#, it''s got to be dead calm before it come out.
As for durability, a guy in Hawaii with the same boat uses his Honda 2hp to motor back & forth between Islands (although I''ve never been in Hawaii when the Trade Winds wern''t blowing at least 10-15k).