Hey Bc
I've had boats since I was 13, and I've bult some. On every motor capable boat there is a DOT plate describing how many people the boat can safely handle and how much horse power it will take. For a 12 it won't be much depending on the hull shape. I'm gonna guess that its like any other standard boat with a point in front, flat at the transom(rear). If it is not and it's square in the front (bow) with a flat bottom all the way, it should not be used in rough water at all. You must always make sure that there is 12" of freeboard when the boat is loaded. Freeboard is measured at the water line to the lowest point of the top of the hull. This will ensure that you won't get swamped by your average wave. Nor should you ever over power a boat either. The manufacturer has built their boats to handle a certain horse power and they know it will run well. Lake St Clair seems way too big for your tiny boat, sorry to tell you that, but you need to know the limitations of your craft. The rating plate probably says 8 or 10 HP, trolling motors are nowhere near that but don't go over the max. No you will not need any kind of licence except your boat operators card.
Boating and fishing are great times but don't risk your life doing it!!!!!!!!!! Too many boaters die each year, the news keeps count, don't be a statistic.