Re: Adding a auxiliary outboard.
I have a Yanmar 1 gm. Personally, I'd go over it well (maybe with a trusted mechanic) and have appropriate spare parts, and forego the outboard idea -- especially with all the trouble you are proposing.
These motors, when in good condition, are very reliable and easy to work on if something does go wrong.
Plus, you do always have the sails as backup power (sorry, couldn't resist).