8hp min
I would say 8hp would work fine. I think thats the one recommended by mfg. I've got a 9.9 sailmaster, and only once needed all 9.9 (the LI race can get 5.5 kts current!) I probably don't recommend the johnson, I've had problems keeping carb clean, water system working, etc., but I did get it used with the boat.You may want to consider the weight factor as well. My '86 25.5 needed stern reinforcing wood on inside of stern to support engine mount. I was getting spider web cracks around the mount points with the original engine mount.