Chin spoiler and rear diffuser really is about all you need from the looks of it. You have most of the other exterior items already.
As far as exhausts, see if there is a drag strip, car meets, etc happening around you. Most people are fine with letting you listen to their setup and most will talk about it for hours. Lol
2016 Mustang GT: Guard Metallic w/ manual transmission; Performance Pack and Backup Sensors