I can tell you your first step would be to test market the area. What area do you plan on serving? Do they already have someone that comes around? Are you going to find a new untapped market in your area or trying to step on someone else's route, compete for established businesses?
In California, almost every place I worked had one of these trucks come by. They had a set schedule, would stay for 20 - 30 minutes depending on size of company and would always leave on time to get to their next location. If you weren't down stairs/outside when the coach arrived, you generally missed out. You, the coach owner, would also have to be on time, it was mutual because the arrival of the coach generally coincided with either break time or lunch time for the company you are at.
You'll need a great short order cook that can work twice as fast as a normal cook. You'll (generally) need a bilingual order taker because the companies that gravitate toward these vehicles have both front office workers and laborers.
Unlike a normal restaurant, you can expect the health inspector to show up without warning at one of your normal stops.
Are you going to buy a new vehicle or a used? If it's used, why are they selling? The advantages, you start at 4 am but you're generally done with your day by 2 pm if not earlier. Start up is not cheap, close to $50,000, at least that was the best information we could find in California, it might be different in New Jersey. It was sort of "if you want to mortgage your home, we can help".
Hope that helps a little. They do make good money after the first year once you've got an established reputation, you may have to give out a bunch of free samples along the way, but if you are determined, you can make it work ~ we just didn't have a house to mortgage to start things up.