As far as the number of things to make... I took a class last year on how to do shows from a lady who makes her living off doing them. She said that after years of this she discovered something neat that others have verified. Don't know if she actually discovered this, or just came to know of it, but it was worth the price of the class.
The 10% rule.
On average, the cost of the show is about 10% of your sales. So…..$150.00 fee = approx $1,500.00 in sales. It’s not engraved in stone, but she said it's surprising how accurate it was when she went back and looked at her historical figures. She also asked other artists to see if this was true for them, and the theory turned out to have some legs! At least it helps you figure out about how much stock to carry when you really have no clue. Of course you'll need more as you always want to have a full booth even if you sell a lot.
One disclaimer...I really don't know how this holds up in this economy. Things are so different right now that who knows. Just got an e-mail today from one of the 3 day shows I applied for. They are cancelling this year due to the economic conditions. This is not a fly-by-night show, but one that's been around for a number of years. I'm hoping it's not a sign of things to come. I don't mind going into shows even if people aren't spending as much as I think it will only help me in the future, but I realize many people cannot afford to think this way. Bummer...