Upload & Sell: Off
It all depends on the use, the smaller the use the smaller the fee, a larger use will be worth more to both the client and you. A picture used by Coke all over the world is worth thousands and thousands of $ while a picture used by Ellen's Flower Shop, not so much.
The License can be as simple as the invoice you write up for them which would describe the picture, how and where it'll be used, for how long and for how much $$$
Remember, there are no ignorant questions but there are plenty of ignorant answers