one thing you should do is make sure its compatable with aa trollmaster or control king before buying the motor. i would contact both places, its the first up grade you will make once its on the back of the boat and you find what a pain going back for the throttle is every minute or two
I think buying a kicker locally would make more sense. What happens when you need some work on it, You will be first in line if you buy locally. If not bought from them they may not treat you the same. Just saying. I would give the guys at Melvin Village Marine like Cool Water said. They know their stuff.
FWIW I had a 20 foot alum boat that went 6 mph with a 6 hp merc 4 stroke. I dont think you need any more than that.
Please contact me for the Controllking unit. If we make one for the kicker you decide on it will be $209. shipped from the manufacturer to your door.
I am the local Rep. for Controllking.