Hey Tubba, we're neighbors!
I'm in Attleboro (I won't go to Bridgewater to set up if you don't come to Attleboro

)
So, let me help you out:
1. You DON'T HAVE to get the ServSafe certification to get the health certificate... IN SOME CITIES/TOWNS. I don't in Attleboro, but if I cross the border (across the street) to Norton, I do. So you do have to call any/all towns you MIGHT think of working in to get that answer.
2. IN ATTLEBORO, only one sink is required on a dog cart. Again, you have to call around to the various Health Depts to see if regulations are different in other towns. Do this BEFORE ordering your cart.
3. FIRST, get the business license from City/Town Hall (maybe you can get the cart first and THEN get the licensing/permits, but I'm getting those first before the cart... someone here can correct me if I'm wrong please). THEN, order your cart, and LAST get the inspection from the Health Dept inspector (he can't inspect if you don't have the cart first, eh!)
See if you can get permission to park the cart somewhere on/near the Bridgewater State College campus.... I'll be if you are persistent/consistent, you'd have a regular crowd there soon.
And lastly, you WILL NEED TO GET a SEPARATE license/permit and health inspection (in MA) for EVERY CITY/TOWN you decide to work in!!! BIG p.i.t.a. I'm starting out just in my own town first this year. We'll see how it goes, and if I feel it's worth the aggrivation, I'll look into other areas. But if I can make my money here in one place (city), it's easier to manage that.
If you are thinking of local fairs, I hope you have a second person in mind to help you out. Doing an event by yourself will be very difficult... ask anyone here.
Let me know if you get set up before April/May... I'll come out and visit you and we can compare notes.
Best of luck