Gee Amy I really don't know how many would be not to many.? Depends on the size of the market and I guess how many other stalls sell cakes etc. maybe you should go along to the market first to see what other stalls are about and how many people go.My friend was going to a market in a small town that had only around 20 stalls and her stall was the only cake stall, she had about 10 cakes, 20 + slices (6 in each), 30 muffins and a few dozen packs of biscuits. I'm only guessing at what I seen.
And i really dont mean to be the downer here, but have you looked at your councils licensing requirements? I know that even to bake for a market in our city your kitchen has to be registered (which is why i dont do it). If the council does a spot check or it someone gets sick from your food fines can be in excess of $10,000 - that's a lot of cakes to make up that fine!
Snappy, the lady who told me about this market used to bake for it as well. She didn't say anything about needing a license, apparently I just need to display the ingredients list of my products somewhere and make sure all the cakes and biscuits are pre-packaged. Do you think I should check with the council though?
Just one extra thing to consider. Insurance for the stall and product liability.