I bought the unit from a company called dynamic sounds. You also need the fitting kit that consists of a facia plate and the plug and play wiring for the unit and steering wheel controls.
The unit is excellent and will only get better as new apps are added.
The volume can be controlled from the steering wheel as well as the touchscreen so there's really no issues with that.
The radio is tuned on installation and then when the radio app is selected you will see both normal tuner buttons and all of your pre programmed stations on small tabs along the bottom of the screen.
It's worth remembering this is effectively a small computer so can be updated and modified to suit your own personal needs.