ST. PETERSBURG — "American Dream,'' Joel Goetz says when he answers the phone. His voice is as smooth and sweet as brown mustard, husky with the tang of 20 years in a kosher deli. In the next hour, he fields 13 more calls from people who want a bite of the dream he's peddling: a new hot dog cart. In hard times, the appeal of low-cost self-employment soars — and a tiny stainless steel restaurant on two wheels gleams. In Florida, more than 150 umbrellas opened over hot dog carts in the last fiscal year, boosting the number of approved...