Welcome, and congrats on your new ride. You are going to love having a truck.

I would go with leveling the truck(+2" up in front, or down in back, but longbeds look better up than down), spray-in bedliner, cat-back dual exhaust. Remember, in most cases, less is more. If you load it down with mods, it will look like you walked through Pep Boys with a magnet, and bought anything that stuck.