rclone actually rocks, I take it back
I just got rclone configured (with my own GDrive API key, a local 4G writes cache, and all the other fixins), and it works better than I thought it would. I've got my Navidrome media folder pointed at it now, with a couple albums in FLAC uploaded to it for testing, and even with transcoding off it seems to work without hiccups.
The thing that tipped me in favor of trying it was realizing that my second Google acct has 100GB of its own that's completely unused, and which I don't think is tied to any temporary bonus storage offers (like the extra storage on my other Google acct, which I think is from a 1-year storage offer with my old Chromebook).
Something else I realized: when I do eventually get that 1TB of storage on the host's internal network, I can use GDrive as a second destination for backups (the provider has their own backup service for like 50c/mo, which I haven't signed up for yet but probably will).
Now I need to get rclone set up on my (Windows) laptop, so I can copy all my FLAC to GDrive without using this box itself as an intermediary, which is thrashing my disk and network unnecessarily. It's not slow, just slightly disconcerting to be pushing bits through so many layers.