You should double or even triple up that sheet metal. 16g is too light in my opinion. It will move under load and make getting a reliable chain difficult.
Maybe a sandwich of stout plywood and sheet metal?
Tin snips will work fine for cutting 16g. There are three color handles, green, yellow, and red. One cuts left, one right, and one straight. Using the correct snip allows straight, perfect edges on your cuts with no further attention, except the straight cut. It usually leaves a slight burr. Use the set that allows you to have all the metal distortion from the snip jaws outside your cut line.