Ideally, you want to move the USB to your Roon core (Windows 10) machine and then add the media through Roon settings (https://kb.roonlabs.com/FAQ:_How_do_I_import_music%3F.) The RPi is your network player or Roon end point and plays music sent from Roon core.
Check out https://kb.roonlabs.com/Roon_User_Guide for more information on using and setting up Roon.