Optional toppings. Spoon on some giardiniera. If you wish, you can top it with marinara sauce, and/or shredded mozz, and melt it on indirect heat on the grill or under a broiler. But never use mustard.
About the olive oil. In Chicago they load up the sangwitch and make sure plenty of the oil gets on the bread and sausage. If there's any of this flavorful elixir left, fry your eggs in it the next morning.
About the bread. Italian bread is a spongy high gluten loaf with a medium hard crust. You can cut it from a large loaf, or buy it in pre-formed rolls. In Chicago, Turano Bakery and Gonnella are the standards.