If I wanted to restart my PC, should I first stop the node

Only the audit stats, but there are better sources for that. This script isn’t meant to determine disqualification risk. It’s meant to gauge performance of your node.
You can use the dashboard API, earnings calculator or windows GUI toolkit to see the stats that the satellite used to determine your audit score.

This isn’t necessary. Windows let’s services shut down cleanly before shutting down or restarting.