You will need to order all wiring and 2 junction boxes, A & B as well as a battery assuming you are starting from scratch. If you are going to have the typical under stem A box, just take a tape measure and wrap it along the bars to your stem and allow for a bit of slop. The wires come in a variety of sizes and the prices don't vary much so I typically round up. The shifter to A wires are easy to hid on the underside of the bar if they are longer than you need and you will never feel them under bar tape..
