The first step to take before even considering franchising any sort of business concept is to open one or more prototype units and see how they perform. (See below for details on what prototypes are and how they work.) This gives you a chance to test the demand to make sure the business concept can succeed in the market, which may directly answer your questions about eating trends, and it also allows you to test and perfect all the main components of the business. These would include the product and menu choices, the unit design and fixtures, the advertising and promotion efforts needed to drive enough customers to the business and the pricing that you’ll need to have to produce a good profit level.
Anyone considering buying a franchise is going to expect to see all these sorts of things completely in place with a strong track record of operational success in the prototype(s) for at least a year or more. Once you’ve completed all the preparation work, you’ll not only be ready to franchise but the questions you’re asking will all have been answered by your prototype operation.
For reference, a prototype is simply a physical representation of the product idea. If the intent is to have this be a kiosk or food truck type of business, then you’d build a kiosk or outfit a food truck with what you have in mind. If it’s going to be a store front retail or food court operation, you’d lease a space and build it out as you think the business should be. The idea is that you’re going to have to risk your money to prove that your concept is valid in the marketplace, so you have to create one or more operations that you’ll run for a while to prove that your concept works. Of course, if it turns out your idea isn’t one that will be successful in the marketplace, then you’ll probably lose your investment, but that’s the risk of starting any new business.