Street Food Tour For New Restaurant
Truck: Honest Tom's tacos (especially fish tacos.) There are several Indian restaurants that serve "street type" fare. I would suggest perhaps hot breads in Montgomeryville, and Indian Hut on Street Road in Bensalem to get ideas of street food, fast food in the indian mode.
Aside from local specialties, Philly's got a decent representation of international street foods. You could hit:
-Solo, the chinese kebab shop on 10th near Arch
-A Banh Mi shop (like QT, which is on the same block as Solo)
-A taco truck (in adition to Honest Tom's, there was a very authentic truck parked at 4th and Washington for a while; if it's still there, it could be worth a visit), or one of the taco joints near the Italian Market--somewhere where you can sample not just tacos but tortas and cemitas too.
-A Caribbean food truck, like the one across from 30th St Station where Bolt Bus picks up, and/or the Jamaican Jerk hut on South St.
-Falafel, like the famous truck at 20th and Market or a place like Maoz
-The Desi Chaat House on 42nd St. in W. Philly, specializing in the Indian street snack chaat
-Maru Global on 10th near Locust, specializing in the Japanese snack takoyaki--little stuffed crepe balls topped with bonito flakes, seaweed and sauces.
That's a start. Have fun eating, and good luck with your restaurant!