You'll probably want to had a few buttons or a keypad too for control (play/pause, next, prev, etc) and maybe an analog input or two for the lcd and volume.
I actually have a very tiny usb thumbpad that's going to be handling all the input to the computer, the volume will be controlled by the head unit in the car (computer will be turned all the way up, and I will adjust the volume on the head unit as necessary)
Thank you all for the tips, going to decide which methods I'm going to use and start sketching things out today.