How long is a piece of string? Seriously, for local gigs I could pull that trailer with my 4-cylinder Ranger at low speeds on surface roads in bottom country and it would be fine. If you're going to sell at festivals and fairs all over the mountain west on the other hand, you need a 6 or 8-cylinder turbo diesel for the same trailer. Diesel for mileage and long life, not because it is more powerful than gas per se.
A 16' trailer is probably way more than you need for two deep fryers and a flat top + prep & cleanup. A 16' trailer is at least 5' longer than a 16' step van (strange but true) and even a 16' step van may be more than you need. A 16' trailer is immense. Festival spaces are sold in 10' blocks--with a 16' trailer are you going to have to buy 3 spaces rather than 2? Go maneuver a 16' trailer between competitors parked 20' apart before you answer me. The competitors are not going to shift and make things easier for you. =^)