Couple wiring questions

Ford solenoid is used to keep the starter battery feed wire dead except during cranking the engine. It's a long tortuous path for a big cable to go from the battery in the trunk all the way to the starter. So to prevent any meltdown as things wear, etc, the solenoid allows it to be hot only during crank.
As for the NSS, I always figure why not use the one in the trans. The one in the shifter can work but the trans one is quite simple and durable.