I regularly motor 15 minutes to a reliable morning thermal on the main lake, and thus have used small outboards on an H18M, SC20, ARC22, and Flight Risk. The bigger boats carry the weight just fine, I'd move crew fwd some on the 18 to compensate for the extra weight aft. I generally use 2 to 3 hp two strokes because they're lighter than four strokes, but the 2hp Honda was a nice motor, noticeably quieter. I generally construct the motor mounts, and they all have the feature that allows the entire arm to pivot upward to allow the lower unit to be parallel to the water when the motor is up, to clear the chop. Important on the 18 and other cats where the rear beam is not far above the waterline.
Motors are definitely additional hassle, but if they allow you to get to the fun, they can be worth the effort.

Dave