First bit of advice: dont buy any electrical connectors off of amazon, they're mostly garbage. I use Vintage Connections, they have OEM spec wiring (although 18GA stranded copper wire is typically all the same) and good quality connectors/tools.

If it were my bike, and I wasnt concerned about anything other than reliability, I would only fix it back to the original wire. Cut out all of the splices and run one piece of wire from the OEM loom to your turn signal connections. Bullet connections are fine, even in-line. Just make sure they still have the plastic sheaths, those help with weather proofing it.

I dont believe most turn signal connector wires are wrapped in factory looms, but for general wire harness use, I love TESA TAPE. It stays stuck, and it doesnt get goopy if it gets hot.