Jackiee19, if you are going to be on Longboat Key, you must go shopping on St. Armand's Circle. It is located to the south of Longboat Key and to the West of Sarasota. It is really a large traffic circle with a beautiful park in the middle and wonderful shops, galleries and lovely restaurants around the perimeter. My favorite restaurant is the Columbia. It has terrific upscale Cuban and Spanish food (try their Columbia salad, delicious!). For shopping, I like the Foxy Lady. You will find many resort wear type shops (Tommy Bahama type stores) on St. Armand's Circle as well as preppy clothing stores. My family loves it!
As for the most up to date shopping stick with NYC. You will pay the price but the selection can only be compared to shopping in Paris or Milan (the prices are comparable to those cities as well). In NYC I have found some unique and beautiful offerings at Daffy's and Century 21 although I do have a problem with the way the merchandise is displayed. Would it really be so difficult for these stores to try to steam the garments before hanging them up?
You have picked two wonderful areas to visit in the US. Have a great time!