Can't answer on the vibration but I have a 12.6 Seaeagle powered by a 77Lbs 15 HP (2 stroke) Mercury. It's managable. I'm by no means physically built, haven't exercised for the most part of my life and I can manage the outboard alone, granted, I don't carry it for a mile! Mostly it's load-unload, the boat has wheels so I it's a short trip from the trunk to the boat and then easily taken to the water. So, if carrying weight is an issue, I don't think 81Lbs would give you much trouble. You'd need to be a bit more careful given the oil issue. When it comes to the outboard, get the largest option you can get, then you won't have to look back and guess what if ....

HTH,