Why oh why do you need to reinstall Windows that often?
Tip: get a second hard drive or SSD and move the Plex data folder onto it.
Next time you want to reinstall Windows, unplug this special hard drive, install or refresh Windows, plug it back in, install Plex server, change the preference where Plex has to look for its data.
See Moving Metadata on Windows
You might also want to give this a look: PSA: Script to back up and restore Plex app data on a Windows system
