I would encourage you to develop a complete wiring diagram before you start wiring. That will really help keep things straight and make sure you do not miss anything. It will be especially helpful when you are troubleshooting the wiring.
I also encourage you to contact others who have converted to LED taillights and turn signals. You may already have done this but they requires a special flasher which will work with the lower current draw of LED's compared to filament bulbs. The flasher does not reduce the voltage.
I would be cautious about supplying power through 2 leads to the same circuit. It might create some feedback loops that will cause undesired results.
You might consider adding a relay to your headlight circuit. Halogen headlights can draw a lot more current that regular headlights. It could be too much for the headlight switch and wiring.
