Congratulations on your first teardown. I hope you took care not to poke around the capacitor without first discharging it. It can hold a charge for a long time without a power source, and touching the terminals with your finger is not a pleasant experience (yes, it happened to me).
There is really no reason to disconnect the upper display LCD ribbon cable. It is somewhat difficult to re-attach properly. If not attached properly the DS will not boot. The lower LCD/digitizer assembly can be removed without the need for Step 16.
This repair is somewhat difficult. There are a couple of points to be careful about:
1) The display ribbon cable is fairly easy to remove from the hinge, but somewhat difficult to route through it once the new display is in place. It is easier to do if the antenna/microphone wires are out of the way.
2) The ribbon connector is fairly short and difficult to manipulate so that it mates securely to the socket on the motherboard. If it isn't seated properly the DS will not boot. So test it first (by temporarily pressing the battery against the battery connectors and turning power on) before re-assembly.
There are 2 screws at the back corners on the bottom cover that are holding the screen down. They need to be removed in order for the screen to be lifted.