… I do not plan on just selling US dogs – they will be my premium product. I will also sell much more affordable Herta franks which are already popular in supermarkets… I believe that the availability of a range of toppings as well  as seeing a NY cart will add a new attractive alternative to what is currently on offer…

I think it is a good idea to sell a hot dog that is already popular with your potential customers.  A great deal of the population does not feel comfortable trying something new.  Having the “new” dog will tempt them when they buy the “old standard”.  Watch your toppings.  You need to keep them fresh and tasty.  We do not sell a “special” dog but it’s amazing the folks who prefer our dogs because our toppings are considered fresh (I chip up sweet onions about once a week and store in the refrigerator in 8 oz zip lock baggies).   We are now using a finely shredded real cheddar cheese… it’s seems more popular, easier to put on and keep on the dog (melts nicely in the hot chili). Listen to your customers and keep a notebook on what toppings they ask for and how often.   

BTW, where will you be set up? My daughter has a friend who lives in  Wolverhampton. He visit London a few times a year.  She would like him to see a hot dog cart (she works our cart at times).