My choice #1...Blair hole saw, drill a pilot hole the size of the arbor....DO NOT rely on a spring loaded arbor pin
#2 Use a step drill as already mentioned, again drill a pilot hole, about 1/8" first.
Another good choice would be a greenlee hole punch if you could borrow one, and if you have back side clearance.
worst choice in sheetmetal is a twist drill
And tape the area, as mentioned...and don't be scared
just Git er done
Mike