Hey Ozzy! A hard drive can be partitioned to appear as multiple drives instead of a single drive (i.e. a 5TB drive can be single partitioned with its full storage as D:, or be partitioned to appear as multiple smaller drives such as D:, E:, and F:) Sounds like yours is in the standard single partition, folders are not an issue.
However while I believe the Lumin will recognize a hard drive like yours connected via USB, to have full indexing and metadata display they recommend that you run MinimServer which is free server software. So I think you’d be best off connecting the drive to a PC on your network and run MS on the PC to support that drive, or else use a NAS drive instead of a USB drive and run MS on the NAS drive.
I don’t own a Lumin myself but this is from what I’ve read about them. I’d suggest discussing your setup with a Lumin dealer to ensure how it will work with your current drive, what limitations is might have, and how to set it up with MS if needed as I know Lumin recommends.