App Radio 4 Help

[V8Killa]

So I'm going to have an App Radio 4 w/ backup Camera added to my 2012 Camaro 2LT RS and I have some questions.

To get started I have the

App Radio head unit
Male to Female USB Connector
iPhone Charger Cable
The harness the App Radio came with
The navigation things
The microphone
Pioneer Camera and the cords

I'm wondering what else I nee to order?

I'm looking at the Scosche dash kit, the ground bypass, the onstar modue, steering wheel controls.

The professional guy at an audio shop told me I needed the harness for the car, am I correct to assume that the harness is the steering wheel control harness?