A lot of these questions are so dependent on where you're talking about operating that they're going to be impossible for anyone reading this thread to answer. Hiring somebody to man a stall in central London is going to cost you >> more than one in North Wales, for example. You may also find that there's an obligation to man the stall at all times, which could mean that one person is not enough (since they are going to need toilet and lunch breaks, at a minimum).