Nice to see another 'experimenter'! I have no doubt that all the concerns raised are valid and well meant, but let me offer a word of encouragement. I move a 14000# 35' sailboat in and out of the marina with an electric outboard. Rather than install it all on the outside, I built an outboard well in the aft lazzrette. It's lifted up out of the water with the topping lift rigged to the backstay, and mounted to a custom built bracket and covered with sunbrella.
Resale value? probably not too much worse than the A4 it replaced! And a whole lot less trouble...
Claw me off a lee shore in a gale: not gonna do it.
Bounce out of the water if rough: Yep.
Me: try to stay out of those situations.
Advantages: No fuel problems. No water growing wierd things in the fuel. No A4 carburetor! No prop drag when sailing. Quiet! Clean! Room for more people friendly items in the boat where a smelly engine used to live.
I also left the old engine in for a while to make sure it all worked. Once sea (bay!) trials were done, out came the Atomic to a new owner on Ebay
Anyways, out of the hundred strange looks you'll get on the dock, once in a while someone shows up to marvel at your backyard engineering ability!