I have a 10' Watertender skiff, with a clamp, seat, oars, and the usual gear. I used a Minnkota 40 electric motor and it works great. Will I take the boat out in strong winds? No. But I take the boat out on decent sized bodies of water and it moves around fine. I do suggest one thing: get an anchor. I like to position my small boat so that I drift but sometimes if there is a bit of wind, I mushroom anchor it so I doesn't move.
I am sure you could go bigger, I know the guy who had my boat before me put a 5hp motor on it and went pretty good. But I honestly don't need more than what I have. So while my answer may not be your answer, just know that it works well.