Although I am not in the business, my wifes company sells to hundreds, maybe thousands of restaurants. They also sell to many other sectors of the food business as well.
The one thing I can tell you from her perspective is, don't get too big before you can afford to do so.
Bottom line, on average about 30 restaurants a year fold and simply do not pay the bill they owe to her company. She sees them making money, but they either buy too much other stuff or a second location and then can no longer maintain the money they owe out.
We know several friends that have very successfully locations. The one thing in common is that they practically live there. I don't know the amount of hours they work, but rest assured it is PLENTY. I am guess 70 hours a week or so.
They never take vacations and lose almost all family time. That said, they are making it and doing well financially.
Hope this helps from a different angle...