Please reference the bash code example of syncing folders from one drive to another under WSL here:
https://github.com/jasonmccb/myWSLSync.git

1. USB disk needs to be mounted MANUALLY from time to time

   sudo mkdir /mnt/e
   sudo mount -t drvfs E: /mnt/e
   sudo umount /mnt/e
   

2. WSL may not be able to read correct permissions from time to time
   Below screenshot shows different results of running same command between a few seconds

   Solution:
   Manually add permission to such folders/files.

    sudo chmod a+r,a+x folder1 file1
    sudo chmod -R 777 folder2	#-R for recursion
   

3. File or folder name can contain % symbol
   This can be a problem to some commands such as find . -printf "$fileName=%f\n".
   When bash expands $fileName, it may considers %xxx as a directive.

   Solution:
   Use %% as % in variable for the “find -printf”.